Abstract: In order to improve the inhibition activity and light stability of the protein extract TraT2A from the fermentation broth of Trichoderma atroviride T2 strain, the ultraviolet protective agents (ascorbic acid, humic acid) and the auxiliary agent (IE-08, SP-4821A and SP-4821B) were screened, the inhibition condition of TraT2A for Alternaria alternata were optimized through the colony growth rate test, and the field control efficacy on lily leaf spot disease was determined. The results showed that TraT2A had a good inhibitory effect on A.alternata at 200.00 mg/mL and the inhibitory rate was 72.12%. With the prolongation of the UV illumination time, the inhibition activity of TraT2A gradually decreases. The addition of 5.00 mg/mL humic acid had an excellent UV protection effect on TraT2A and its inhibition rate (69.01%) increased by 39.64% compared with that without a UV protection agent (29.37%). The addition of 0.17 mg/mL adjuvant of SP-4821A increased the inhibition activity of TraT2A most significantly and the inhibition rate (95.13%) increased by 25.97% compared with the TraT2A control (69.16%). According to the optimized formula, 200 g TraT2A (the mass concentration was 200.00 mg/mL), 5 g humic acid (the mass concentration was 5.00 mg/mL), 0.17 g SP-4821A (the mass concentration was 0.17 mg/mL) and 794.83 mL sterilized water was mixed and the field control efficacy of the mixture was tested on lily leaf spot disease, the result showed that its field control efficacy was 80.37%. The research results provide a theoretical basis for the further development of TraT2A preparations for the control of lily diseases.