Aiming at the welding problem of steel used in automobile, the microstructure and property of joints in laser welded tailored sheets for dissimilar steel with different thicknesses are analyzed by optical microscope (OM), scanning electron microscope (SEM), hardness and tensile test. The results indicate that weld zone are lath martensite, and the laths mixed with retained austenite. Microstructure near the fusion line is more complex, mainly consists of martensite and bainite. Heat affected zone (HAZ) of transformation induced plasticity (TRIP) steel is mainly composed of bainite and ferrite, and the grains are relatively small. There are significant martensite existed in HAZ of dual phase (DP) steel, and the overheated zone is almost non-existent. The hardness in weld zone is more than 1.6 times as the parent metal. Macroscopic fracture of joint occurs in base metal of thinner DP steel sheet.