Abstract: Single-L and double-L composite joints were designed with similar weights. A combination of experiment and numerical simulation was used to study the tensile failure mechanism of the two joints. Two kinds of L-joints were quasi-statically loaded to failure on the servo hydraulic testing machine through a self-designed test fixture, and the failure mechanism and strain distribution were analyzed. It’s found that the two L-joints have different failure mechanisms, and the single L-joint exhibits better ductility in the failure stage. When the single L-joints are loaded to the peak load, the damage first occurs near the inner bolt hole in the loading side, and then the damage spreads to the outer bolt hole until failing completely. When the double L-joints are loaded to about 50% of the peak load, the adhesive film between the L-shaped frame and the L-shaped sheet is first damaged, and then when the load continues to increase to the peak load, damage occurs near the bolt holes of the L-shaped frame, extending to the edge of the frame, the load drops significantly. In addition, the strains of the two joints have different trends with the increase of load. Based on a new type of composite material initial failure criterion and stiffness reduction method, a user-defined material subroutine (UMAT) was written. Combined with the cohesive zone model, the progressive damage model of the composite material L-joint was established. Based on ABAQUS software for calculation, the predicted failure load and failure mode of composite single L-joint and double L-joint were obtained. The results show that the damage position and failure mode of the composite L-joint obtained by the finite element analysis are consistent with the test, and the predicted load is slightly different from the test value, which proves the applicability of the finite element model.