A mathematical model of TR (Time Reversal) power combination in the slowly time-varying atmospheric channel and the concept of channel time-varying factor are proposed to study the feasibility of TR technique for spatial power combination in incompletely reciprocal channels. Combining the theoretical analysis and Monte Carlo simulations, we analyze the relationship between the power combination efficiency and the permittivity of the time-varying atmospheric channel, which follows a normal distribution. In this data file, simulation results obtained by commercial software MATLAB are listed. The results indicate that the power combination efficiency of the TR technique will be lower than that of the completely reciprocal channel if the atmospheric channel is slowly varied, and the faster the channel changes, the lower the efficiency becomes. In order to keep the power combination efficiency above 50%, the channel time-varying factor needs to be less than about 54.3% of the signal period. And when it takes more than 90%, the signals radiated by each antenna have been completely incoherent at target point.