The midium wave (MW) HgCdTe avalanche photodiodes (HgCdTe APDs) were prepared by two different processes. The pn junction characteristics and the relation between gain and bias voltage for HgCdTe APDs were characterized by two different methods. The gain-bias curves of APDs were fitted based on the Beck model and Shockley′s analytical expression. The results show that the widths of the saturated depletion region for APDs fabricated by two different processes are 1.2μm and 2.5μm respectively. The wide depletion region effectively suppresses the tunneling current at high reverse bias. The effective gain of the device increases from nearly 100 to over 1000. Shockley′s analytical expression gives an excellent fit to the gain-bias curves of HgCdTe APDs, and the fitting parameters are similar to the results of J. Rothman at Sofradir.