Mg2-xSnxNi (x=0, 0.05, 0.1, 0.15, 0.2) hydrogen storage alloys were prepared and the effects of substitution of Sn for Mg on hydrogen storage performances of the alloys were investigated. In the alloys, Mg2Ni is main phase and the amorphous degree increases gradually with amount of Sn content increasing. Partial substitution of Sn for Mg can change the temperature of hydrogen absorption reaction effectively. The Mg1.85Sn0.15Ni alloy absorbs hydrogen at about 330K which is about 80K lower than that of Mg2Ni alloy. Discharge capacity increases quickly with amount of substitution Sn for Mg increasing. Suitable amount of substitution of Sn for Mg and amorphous can improve the thermodynamic and electrochemical characteristics of hydrogen absorption reaction for Mg2Ni-based alloy.