Nd:YAG laser was used to weld 2 mm thick tapes of NiTi shape memory alloy (SMA). The effect of main welding parameters including laser power, welding speed, defocusing amount, gas-assisting blowing on weld shaping was investigated. The results show that appropriate matching of main welding parameters is the key of realizing good weld shaping. Linear heat input between 59～75.6 J/mm can acquired optimal formation of welds. The defocusing amount between -2～3 mm can relize full penetration of 2 mm thick tapes of NiTi alloys. The defocusing amount between 0～1 mm can obtain the optimal formation of welds. The protective effectiveness and the weld formation is the best when side-blow shielding gas flow rate is from 15 to 20 L/min. Different matching of laser power and welding speed effecting on different formation of welds were experimentally acquired which supply references to laser welding and engineering application for NiTi alloy.