For the problems of low sensitivity and poor adaptability of existing robot hand collision detection device, a variable stiffness robot collision sensor with inertia adaptive function was designed based on the variable stiffness hand inertia force compensation mechanism of electromagnetic force servo. The collision trigger force threshold of the sensor changed adaptively with the robot hand inertia force to eliminate the influence of inertia force on collision detection and to improve the sensitivity of collision detection in real time. The results of the collision experiments show that the electromagnetic variable stiffness method can significantly reduce the compression force of the sensor preload spring, improve the dynamic detection sensitivity of the robot end-effector collision process, and then enhance the intelligence of robot collision detection and safety protection in human-robot collaboration.