In this paper, we studied the relationship between dark current and baking time of mid-wavelength HgCdTe infrared photovoltaic detector. A simultaneous-mode nonlinear fitting program for n-on-p mid-wavelength HgCdTe infrared detector is reported. The curve-fitting model includes the diffusion, generation-recombination, band-to-band tunneling and trap-assisted tunneling current as dark current mechanisms. The dark current components and six characteristic parameters were obtained from the fitting of resistance-voltage(R-V) curves measured before and at different annealing time. The effects of annealing on the performance of the photodiodes were analyzed by comparing the characteristic parameters of devices at different annealing time.