Thick laser coating on sealing surface of high parameter nuclear and chemical valve have been made, And the factors that will influence layer’s cracking behavior have been analyzed including laser cladding material, technology and base metal. It is approved by experiment that the greater the energy ratio is, the lower the possibility of cracking would be. But this case may cause diluting rate of the coat increasing, grains coarsening and hardness reducing. B and Si can create hard phase, reduce coating’s plasticity, and generate segregation easily in Ni-base alloy which may cause crystal crack. The rate of coating cracking will reduce when substrate has homogeneous structure, no relict stress, no defect, good plasticity, and, its rate of heat expansion is a bit higher than clad material, heat capacity is small, shape and structure is simple and heat symmetrical characteristic is good.