Abstract: As uncertainties inherent factors，such as temperature and wear, always exist during wet multi-disc brake’s lifetime, a time-dependent model was established，which incorporating such uncertainties based on stochastic differential equation theory. The time-dependent design method for wet multi-disc brake under such external uncertainties factors was presented. This method takes the braking distance and temperature changes with time into account. It can evaluate dynamic security reliability for wet multi-disc brake products, which reflects the impact of time scale in the design. The brake that can meet the reliability requirements at any time can be designed by the new method, which can provide a reference for dynamic security assessment of brakes reliability.