A three-point bending test of hot forming high strength steel specimens with different thickness was designed. The related mechanical parameters were obtained. The results indicated that the bending mechanical properties of hot forming specimens were strengthened with the increase of the thickness. The specimens which were based on different thickness had higher center hardness and lower surface hardness. Meanwhile, a multi-layer composite material was proposed with hardness gradient distribution in the direction of the thickness. Based on the hardness gradient and the hardness-strength corresponding to the relationship, a multi-layer gradient numerical simulation model of three-point bending was established, explored that the gradient material model was more rational for numerical simulation. 