The experiments of laser welding were carried out for AZ31B magnesium alloy and DP590 dual-phase steel in an overlap magnesium-on-steel configuration with interlayer addition. The interlayer elements were selected based on the calculation of thermodynamic properties and intrinsic mechanical properties, and the changes of microstructure and properties of magnesium/steel joint were analyzed. The results showed that with the addition of Sn and Al interlayers, the maximum load of the joint was 730 and 590 N, respectively, which was 2.04 times and 1.46 times higher than that without interlayer. With the addition of Al interlayer, the brittle Mg₁₇Al₁₂ compound was formed at the magnesium/steel interface, which limited the improvement of the mechanical performance of magnesium/steel joint. In the case of adding Sn interlayers, Mg₂Sn with relatively low brittleness and Fe₃Sn with a certain ductility were formed at the magnesium/steel interface, which was a vital reason that the properties of joint with Sn interlayer were higher than those with Al interlayer.