Abstract: Taking ‘Tianhong 2/SH38/Malus micromalus’ apples as test materials, the method of ammonium thiosulfate spraying was used.Water was used as the control, and 1.5% ammonium thiosulfate was sprayed twice during the initial and full flowering stages.After 7,10,13,16 days and 19 days of spraying, treatment and control side fruits were collected and treated.The effects of ammonium thiosulfate on nitrogen, phosphorus, potassium mineral nutrients, starch, glucose, fructose, sucrose and sorbitol, soluble protein, zein, gibberellin, auxin, abscisic acid, and ACC content in apple side fruits were studied, their removal mechanism was preliminarily analyzed, in order to provide reference for production.The results showed that the total N content of the treatment was higher than that of the controlafter ammonium thiosulfate treatment, while the total P and K content significantly decreased in the middle stage of treatment.The starch content of the treatment was increased by 5.13% to 22.64%,while the content of sucrose, glucose, fructose and sorbitol were decreased in different degrees, resulting in a decrease in the total soluble carbohydrates content by 9.37% to 19.90%.After ammonium thiosulfate treatment, the content of abscisic acid and ACC significantly increased, and there was no significant difference in the（Z+GA₃+IAA）/ABA ratio between the treatment and the control.As a result, ammonium thiosulfate had a good fruit thinning effect on apples, related to the decreased soluble protein content, an insufficient supply of soluble carbohydrate, increased ABA and ACC content.