The work aims to study effects of Mg3Sb2 on microstructure, hardness and tribological properties of Al-Mg3Sb2 composite coatings and compare differences in properties of AZ31B magnesium alloy substrate, pure Al coating and coatings doped with different content of Mg3Sb2. The Al-Mg3Sb2 composite coatings were prepared on the surface of magnesium alloy AZ31B by flame spraying. Cross sectional morphology of the coatings were observed with SEM. Phase composition of the coatings was analyzed with XRD. Microhardness of AZ31B and the coatings was tested with microhardness tester. Tribological properties of AZ31B and the coatings were measured with friction-wear tester. And width, depth and wear volume of grinding cracks were measured with ultra deep field 3D microscope. Dense composite coatings could be obtained by flame spraying, and phases in the coatings were mainly Mg3Sb2 and Al. Average microhardnesses of the coatings increased with the increase of Mg3Sb2 content, which was up to 334.2HV0.025, which was 4.14 times that of AZ31B. In the friction-wear test, friction coefficient of the coatings decreased with the increase of Mg3Sb2 content, which was greater than that of AZ31B. Wear rate of the coatings decreased with the increase of Mg3Sb2 content. Wear rates of 60% Mg3Sb2 and 80% Mg3Sb2 coatings were less than that of AZ31B, wear rates of other coatings were more than that of AZ31B. Compared with AZ31B, wear rate of the 80%Mg3Sb2 coating decreased by 63.26%. With the increase of Mg3Sb2 content, worn surface furrows on the Al-Mg3Sb2 composite coating become shallow and disappeared gradually. The addition of Mg3Sb2 can improve hardness of the coatings, and wear resistance of the coatings increases gradually with the increase of Mg3Sb2 content.