【Objective】It is well known to all that earthworm cast helps soil aggregation and hence affects significantly physic-chemical properties of the soil. The cast earthworms produce on surface of the soil makes it rougher, thus affecting water infiltration. However, little attention has been given to impact of the earthworm cast on soil surface on soil water evaporation processes. In this paper, a simulated evaporation experiment was carried out to explore effects of earthworm cast mulch on soil evaporation. 【Method】The experiment was designed to have two variables, thickness and coverage of the cast mulch, i.e. 1 cm, 2.5 cm and 4 cm for the former and 30%, 60% and 90% for the latter, and a control, i.e. a plot of bare soil. All the treatments, including the control, in the experiment, were monitored for 15 days in a row for daily evaporation and 12-hour or diurnal change in evaporation. Daily evaporations were recorded and accumulation of the 15 days calculated for analysis of differences between the treatments. In addition, samples of the soils and earthworm cast were collected before and after the experiment for analysis of organic matter content.【Result】Results show that the ratio of soil evaporation to atmospheric evaporation was lower in the treatments than in the control and declined with increasing thickness of the mulch (4 cm < 2.5 cm < 1 cm < bare soil). The cumulative evaporations from the soil mulched with 1 cm, 2.5 cm or 4 cm of cast were 10.66%, 14.19% or 33.38% lower than that from the control, respectively. The daily monitoring shows that soil evaporation varied with temperature; the thicker the mulch and the lower the soil evaporation. In the bare soil, evaporation peaked in the first five days of the experiment and then declined down to a level lower than that in all the other treatments in the days to follow, which might be attributed to the rapid loss of soil water in the early days, making the surface soil compacted. And the compacted soil surface hindered soil evaporation. The cumulative evaporation in the soil mulched up to 30% and 60% was 0.17 and 0.07 time respectively, higher than that in the soil mulched up to 90%, indicating that soil evaporation decreases with rising mulching coverage. In terms of daily variation of the evaporation, the treatments exhibited an order of 30% > 60% > 0% (bare soil) > 90% in mulching coverage. The mean cumulative evaporation of the soil mulched up to 90% was 89 percent of that of the bare soil, indicating that the mulch of cast inhibits soil evaporation. The earthworm cast was 3.53 times as high as the soil in organic manure content before the evaporation. Along with the progress of the experiment, organic matter content decreased in both earthworm casts and soils in all treatments. But the soils mulched with earthworm cast were significantly higher than the control in organic matter content after experiment, showing that the higher the thickness and coverage of the mulch, the less the decrement in soil organic matter content.【Conclusion】It can be concluded that mulching earthworm cast on soil surface helps reduce soil water evaporation. For a given mulching coverage, water evaporation decreases with increasing mulching thickness. The effect of mulching coverage on evaporation is not significant due to compaction of the surface soil. Both evaporation and its variation, however, decreases with increasing mulching coverage, indicating that the higher the mulching coverage, the higher the effect on evaporation. Earthworm cast is quite high in organic matter content, and hence higher in soil water retention capacity. That is to say, cast mulching is able not only to increase soil organic matter content, but also to retain soil water. Besides, the mulch can also reduce influences of the external factors, such as climate, thus making soil evaporation and its variation lower.