In order to study the influence of plants on soil evaporation rate and erosion resistance characteristics and the changing rules, two types of plants commonly used for slope protection, ryegrass and alfalfa, were selected for evaporation test and erosion resistance test. The evaporation rate of samples during plant growth period was analyzed under different plant seed proportion conditions, and the vegetation coverage after 14 days of plant growth is obtained by combining image binarization method. The anti erosion characteristics of soil under different plant seed proportion were analyzed. The mixed plant seeds used in the plant growth sample were set with five ratios, the ratios of ryegrass and alfalfa were 1∶0, 0.7∶0.3, 0.5∶0.5, 0.3∶0.7 and 0∶1 respectively, and the plant growth cycle was set at 14 days. The results shows that alfalfa has a more significant effect on soil evaporation rate in the early stage of vegetation growth and development, and the evaporation rate of all proportions of samples tend to be consistent in the stable growth period; Using the method of image binarization, it is concluded that the highest vegetation coverage is 80.1% when the ratio of ryegrass to alfalfa is 3∶7; With the increase of the vegetation coverage of the mixed proportion sample, the developed plant stems and leaves reduce the impact of rainwater on the soil and weaken the runoff erosion. Different types of roots combine with the soil to increase the depth of root influence and enhance the reinforcement effect, and enhance the anti scouring performance of the soil.