The state of orgsno-mineral complex in soils under the rotation of paddy and upland Crops was studied. Soils used in experiment were yellow brown earth derived from siashu loess and grey fluro aquic soil as well as their corresponding paddy soils. 1. A change from paddy field to dryland was advantageous to promote the complexing process and increase the amount of organomineral complex in soils. However, a change from dryland to paddy field could increase the quantity of free organic matter and was advantagenus to the accumulation of soil organic matter. The rotation of paddy and upland crops could improve the state of organomineral complex of soils by accelerating the transformation of organtc matter.2. After a change from paddy field to dryland, the content of tightly combined humus was comparatively increased, it was favorable to improve soil structure. Simultaneously, the liable oxidizing parts of loosely combined and tightly combined humus were increased and it could promote the oxidation and regeneration of combined humus. While a change from dryland to paddy field, the content of loosely combined humus was comparatively increased, it was advantageous to activation of soil humus. 3. The rotation of paddy and upland crops could caused the difference in fractionation end composition of soil humus. The increase of ratio HA-B/FA-B and the decrease of ratio HA-A/FA-A after the change from paddy field to dryland indicate that the laible mineralizable fraction of soil humus was increased and it might be promote to release soil nutrients.4. The contents of C, N, P and S in soil complexes were enhanced with the reduce of Sod complex particle sizes except silty complexes. The change of C, N, P and S contents in soil complexes of different particle sizes under the rotation of paddy and upland crops showed that a change from paddy filed to dryland was favourable to shorten the cycle period of C, N, P and S in sails and make them to be mineralizaed easily.