The contact state of the bolt joint surface has an important influence on the contact stiffness, damping, and other properties of the equipment. To obtain the contact state of the bolt joint surface, the method to detect the contact state of the bolt joint surface based on laser ultrasonic technology is proposed in this paper. The reflectivity under different working conditions is obtained by the reflection amplitude of the longitudinal wave before and after bolt tightening. The relationship between reflectivity and bolt torque is studied. The results show methods proposed in this paper can effectively detect the contact state of the bolt joint surface, and it provides a basis for the study of the mechanical properties of the contact surface.