For the problem of stamping cracking in tailor welded blanks of dual-phase steel with different strengths, the forming process of front beam part was simulated by software Autoform, and the changing rules of material thinning rate, stress and strain at different positions were studied. Then, the influence laws of blank holder force, n value and r value on the weld seam cracking were studied through the single variable test method. The results show that the material at the weld seam is affected by forming force and blank holder force in the early stage, and mainly affected by tensile stress of the displacement for DP780 dual-phase steel in the later stage. As a result, the tensile stress received by the blank at the weld seam is greater than the forming force of DP780 dual-phase steel, causing the plastic strain and thickness thinning rate of the weld seam blank to increase rapidly and leading to cracking. When the blank holder force is optimized to 1500 kN, the parts does not crack, and the simulation results are verified in production. The n and r values of DP780 dual-phase steel have little effect on the thinning rate of blank at the weld seam of part, while the n and r values of DP590 dual-phase steel have a significant impact on the thinning rate of blank at the weld seam of part. When r value is greater than or equal to 1.4 or n value is greater than or equal to 0.19, the part does not crack.