The ratchet effect caused by superconducting vortex motion can be widely used in flux pumps, rectifiers and superconducting switches. Ginzburg-Landau theory provides a powerful tool to investigate superconducting vortex matter. In this paper, the finite difference method is used to numerically solve the time-dependent Ginzburg-Landau equation, and the fast Fourier transform method is used to solve the coupled heat conduction equation. The vortex dynamic behavior of the superconducting thin film with a linear change of critical temperature is simulated numerically, and a new way to regulate the superconducting rectification effect is proposed. The effect of critical temperature gradient and slit location on the reversal phenomenon of rectified voltage are studied. Because of the influence of edge barrier and the defect attraction potential on vortex motion, it is beneficial to observing the reversal rectified voltage with increasing AC amplitude that the defect location is near to the side of the higher critical temperature or the gradient of the critical temperature is small.