Transformation induced plasticity (TRIP) steel is one of the advanced high strength steels (AHSS) group with multiphase microstructure that are replacing conventional steels in the automotive industry because of their very good mechanical properties. Fusion welding methods have challenged their application by destroying of microstructure. Therefore, in this paper two type of spot joining, resistance spot welding (semi-fusion) and friction stir spot welding (solid state), investigated. First, thermal history of metal during both of welding obtained using finite element analysis. Then, TRIP steel sheets joined under same condition of finite element models. Based on the temperature data obtained from finite element analysis and the data obtained from experimental tests such as microstructure (FE-SEM and XRD), microhardness, residual austenite value in the welding zone and the lap shear strength of joints, a comparison was made between the two methods. The microstructure of the weld region in both methods was mainly martensite, but in the FSSW method, some retained austenite also identified. Also, the maximum hardness in RSW was 505 VHN and in FSSW was 478 VHN. It can be related to the lower peak temperature and non-melting and non-solidification during the process, and the presence of some austenite in the microstructure of the weld metal. The maximum temperatures for the FSSW and RSW were 940 and 1900 ° C, respectively. The FSSW strength was 9.8 kN, which was higher than the RSW bond strength (7.8 kN). This is due to the presence of a martensitic microstructure with an appropriate hardness and a certain amount of austenite in the final microstructure.