The forming process of Selective Laser Melting (SLM) involves complex heat change and energy transfer, which changes the temperature distribution and morphology structure of the molten pool, thus affecting the performance of the forming parts. In this paper, a three-dimensional transient model was established by finite element software ANSYS to study the effects of laser power and scanning speed on the thermal behavior of NiTi monolayer formed by SLM. The results show that the scanned area will preheat the unscanned area, leading to the difference in peak temperature between the two scanning tracks, and the peak temperature and size of the molten pool will increase with the increase of laser power or the decrease of scanning speed. When the laser moves along different paths, the laser power has a greater impact on the temperature gradient of the molten pool than the scanning speed. Combined with the experiments, it can be seen that as power and scanning speed elevate, the microstructure of the NiTi alloy formed parts becomes more uniform. However, excessively low power or high scanning speeds can induce pores, impurities, and cracks within the NiTi alloy component's microstructure.