This study simulated amplitude variation in the time varying surfaces effect for an underwater communication testing platform (a wave making towing tank of 176m × 8m × 4m). The interaction between signals and boundaries on the testing platform causes a multipath effect. Meanwhile, surface wave movement from the wave maker induces a Doppler shift, creating amplitude variation in the channel's impulse response (CIR). In the simulation, the channel's boundary interaction is recreated using an image method, and random analysis is conducted to represent the time varying surface. Three variations of surface wave height are observed in order to understand the characteristics of amplitude variation. The received signals are processed by an applied passive time reversal mirror (TRM) to focus the energy and to reduce inter-symbol interference (ISI). The bit error rate (BER) is evaluated by comparing the communication performance of time reversal and non-time reversal processes. The results show that TRM is an effective method to reduce BER due to the multipath effect and the time varying surface effect.