The effect of laser power, scanning speed and powder feeding rate on feature sizes of weld height, weld width, weld depth during laser deposition repair single track GH738 alloy were investigated by orthogonal test; the parameters were optimized and defect-free microstructure was obtained; the reason of defects such as ill bonding & cracks in deposition zone and the characters of microstructure & microhardness were analyzed. The results indicate that the microstructure of GH738 deposition zone is made of columnar dendrites which grow epitaxially from the substrate. Few carbides are precipitated in the interdendrite. Compared with the substrate, the carbide in the heat affected zone is obviously reduced;meanwhile the size of γ′ phase in heat affected zone increases obviously. The microhardness of deposi-tion zone(350-470 HV0.3) and heat-affected zone(450-480 HV0.3) is lower than substrate(480-510 HV0.3),and microhardness decrease gradually along the deposition height direction.