Abstract: Objective: To study the changes of physicochemical properties in Shuidouchi before and after fermentation, and to preliminarily explore the inhibitory effect of its extracts on castration-resistant prostate cancer cells (CRPC). Methods: Shuidouchi was fermented using three high-yielding protease strains. With reference to the national standard methods, contents ofamino nitrogen, total acid, pH, reducing sugar and soybean isoflavones in Shuidouchi before and after fermentation were tested, and total phenol and flavonoids were examined by chemical method. And the antioxidant capacity of Shuidouchi extracts was also determined. Finally, the inhibitory effect of Shuidouchi extracts fermented with the optimal strain was observed. Results: Fermented by high-yielding protease strains, the contents of amino nitrogen, reducing sugar, isoflavone and antioxidant capacity of soybean were all improved compared with steamed soybean, among which B19 strain fermented Shuidouchi had the best effect. And the extract of Shuidouchi fermented by B19 strain could selectively kill CRPC cells and promote their apoptosis, and inhibit the secretion of prostate-specific antigen (PSA), androgen (T) and dihydrotestosterone (DHT). Conclusion: Fermentation by high-yielding protease strains of Shuidouchi can change the physicochemical properties, and enhance its nutritional activities. Moreover, the extract of Shuidouchi fermented with B19 strain has an inhibitory effect on CRPC cells. This study provides data references and theoretical support for the research and development of health functional foods related to Shuidouchi.