The Lajia Ruins is a large-scale settlement of the Qijia Culture (4 200～3 950 a BP). Archaeological excavations have exposed a shocking picture of prehistorical catastrophes in the Lajia Ruins in the Guanting Basin, Minhe County, Qinghai Province. The causes of the prehistorical catastrophes in the Lajia Ruins have become a hot topic in the field of environmental change. Unfortunately, so far little has been reported on development processes and micromorphological features of the ancient plow layer of the paleosol in comparison with the plow layer of the modern soil in the Lajia Ruins. Therefore, a comparative study was carried out on micromorphologies of the two soils in an attempt to reveal their development processes and micromorphological features. Micromorphological features of different genetic layers of the soil profile in the Lajia Ruins were observed under a Leica-DMRX petrographic microscope, and their images was quantitatively measured using Leica-Qwin V3 software. The main micromorphological features of the ancient plow layer of the paleosol of the Qijia Culture (Ah₂/Ap₄) are round to sub-round coarse grains, low C/F_15µm, poorly directive permutation, abundant illuvial clay hypocoatings and concretion, abundant needle-shaped secondary-calcite at edge of pores, high porosity consisting mainly of smooth circular pores and bag holes. The ancient plow layer of the paleosol of the Xindian Culture (Ah₁/Ap₃) is quite similar to the ancient plow layer of the paleosol of the Qijia Culture (Ah₂/Ap₄) in micromorphological features, except for C/F_15µm, which is higher in the former, and proportion of illuvial clay, which is lower in the former. The main micromorphological features of the ancient plow layer of the paleosol (Ah₂/Ap₄, Ah₁/Ap₃) are different from that of the modern plow layer (Ap₁) in the Lajia Ruins. The Ap₁horizon is characterized by sub-angular to sub-round coarse grains, abundant residual clay concretion and a little amount of illuvial clay hypocoatings, abundant needle-shaped secondary-calcite, low porosity, and high C/F_15µm. Both the Ah₂/Ap₄ horizon of the Qijia Culture and Ah₁/Ap₃ horizon of the Xindian Culture are Ustic Isohumisol. They formed in the mid-Holocene Climatic Optimum under simple cultivation of the ancient people and paleoentological climate. The Ap₁ horizon is Calci-orthic Aridosol, a soil formed under the inergrated effect of long-term manure application, crop cultivation and deposition of dust storms during the past 1 500 years. Its micromorphological features are mainly controlled by the degree and manner of human activities.