Surface hardening intergal molding valve seat of a vermicular cast Iron was done by Nd:YAG high power laser. The effect of laser parameters on microstructure, hardness and surface quality were conducted by scanning electron microscopy (SEM) ,optical microscopy (OM) and microhardness tester. The results show that The hardening layer of free defect can be obtained with suitable laser processing conditions. The shape of crescent can be observed in the laser hardening layer.The hardening layer consists of melted zone and heat-affected zone.Ledeburite, martensite and remainder austenite can be observed in the melted zone.The heat-affected zone consists of martensite and remainder austenite with retained vermicular graphite.Laser hardening layer has no-uniformity distribution of rigidity due to no-equilibrium calefaction and cooling.The defect of sunen disfigurement can be restrained by reducing heat-input in the ending zone.