This paper studied soil erodibility of slope farmland in Guizhou mountain areas by the plot runoff method, analysis and test. Results show that the variation coefficient of erodibility K value calculated according to formula introduced by Sharply is low and relatively stable and accurate, so it is a suitable method for calculating erodibility K value of slope farmland in Guizhou mountain areas. K value of layer A slope farmland decreases with increase of years. The erodibility of entire soil layer is high, and the erosion resistance is weak. From the influence of different planting system and use types in 4 years, K values of different soil layers decrease, average reduction of A, B and C layers reaches 3.17%-11.64% (1.26%-12.34% for layer A, 1.29%-13.80% for layer B, and 1.26%-10.80% for layer C). Except engineering terraced treatment, the decline of K value of grassland, zoning crop rotation, economic fruit forest, grain and grass intercropping, plant hedge, and mixed forest treatment is higher than farmers’ treatment, and the decline level is grassland ＞ zoning crop rotation ＞ economic fruit forest ＞ grain and grass intercropping ＞ plant hedge ＞ and mixed forest treatment. Planting grass and trees is favorable for lowering erodibility of slope farmland and improving farmland quality. Interplanting of corns with other plants can increase plant coverage and species, so it is favorable for improving erodibility of slope farmland.