Exploring experiments of the laser hardening valve seat of worm cast iron were conducted.Microstructure of laser hardening region was characterized by optical microscopy (OM). Mechanical properties of the hardening region were evaluated by hardness. Effect of laser hardening parameters on the valve seat of worm cast iron were discussed in detail. Results show that the harded region have non-equilibrium microstructures consisting of martensite and residual austenite with a little ferrite. Microstructure of the martensite shell around the worm graphite in the hardened zone is observed. With increasing defocusing distance ,the hardness of hardened region decrease.The hardness of hardened region can be increased by imporving laser power and reducing laser welding velocity.