Abstract: Objective：To establish a method for determining the bacteriostatic effect of dexamethasone sodium phosphate eye drops and to evaluate the rationality of its use. Methods：According to the requirements of the bacteriostatic efficacy test method of General Principles 1121 of the Chinese Pharmacopoeia of 2015 edition， the applicability of dexamethasone sodium phosphate eye drops was tested by using Staphylococcus aureus， Pseudomonas aeruginosa， Escherichia coli， Candida albicans and Aspergillus Niger as test bacteria， and then the challenge test of microorganisms was carried out. The number of viable bacteria was determined at different time points determined by methodological experiments. Results：Dexamethasone sodium phosphate eye drops can meet the "A" level bacteriostatic efficacy standard. Conclusion：The dosage of antimicrobial agent in dexamethasone sodium phosphate eye drops is 0.02% thiomersal and 0.38% borax. This concentration of antimicrobial agent has strong antimicrobial effect on bacteria and fungi. It is suggested that the lowest effective concentration be used to ensure the safety， effectiveness and stability of the product.