This paper proposes a new equivalent failure strength model for spot welds under combined axial and shear loading. To evaluate the pure-shear strength of spot welds fabricated under the same welding conditions with a two-layered lap joint, a test fixture and a specimen were newly designed and proposed. The failure tests of spot welds of TRIP590 1.2t, DP780 1.0t, DP780 1.2t, and DP980 1.2t were carried out at seven different loading angles ranging from 0 degrees to 90 degrees at an internal angle of 15 degrees to obtain the failure loads. The failure loads obtained from the experiments were utilized to construct the failure criterion and thus describe the failure behavior of spot welds in the crash analysis or strength analysis of an auto-body. It is noted that the value of beta in the failure criterion for spot welds of AHSS is different from the values of conventional steels. The new equivalent failure strength model proposed in this paper was derived from the failure test results to provide a representative failure model that can be used to accurately compare the failure characteristics of different materials under the same conditions.