In view of the loose structure of sand loess in the northern Loess Plateau, the cohesion between particles is small, and it is easy to be damaged by rainwater erosion, MICP technology is used for film mulching protection. The effects of calcium source and treatment rounds on the MICP mulching effect of sandy loess were investigated. Three calcium sources of calcium chloride, calcium acetate and calcium lactate were selected to mulch the slope model under four different rounds. The calcium carbonate content, indoor rainfall scouring test and micro-penetration test were carried out on the samples after mulching. The results show that: Different calcium sources have different coating forms. Calcium chloride and calcium acetate mainly strengthen the soil by increasing the cohesion between soil particles, while calcium lactate is more likely to form a hard shell layer on the surface of the soil to protect the soil. The effects of calcium source and treatment rounds on the MICP coating effect of sandy loess are mainly reflected in the content of calcium carbonate and the curing depth. The effects of different calcium sources on film mulching under different treatment rounds were different. When calcium chloride was used as calcium source, the effect of film mulching was better when the treatment was more than 3 rounds, and the effect of film mulching was not obvious when the treatment was more than 5 rounds. Calcium acetate as a calcium source, the effect of film mulching was poor when treated for 1 round. When treated for 3 to 7 rounds, the effect of film mulching increased significantly with the increase of rounds. Calcium lactate as a calcium source, the effect of film mulching was better when treated for 1 round, but the effect was not as good as calcium chloride and calcium acetate when treated for more than 3 rounds. The research results of this paper can provide some reference for the protection of sand loess slope erosion in Ordos area.