High-voltage cable joint short-circuit arcs can easily cause explosions and fires, resulting in secondary damage, so protective devices need to be installed. The irregular structure of the protection device leads to the deformation of the stress distribution, which becomes the weak link of explosion protection. A method to improve the safety margin of cable joint protection device based on equilibrium stress distribution is proposed. Using the explosion source equivalent method and the finite element calculation method of coupling temperature field, magnetic flux field and displacement field, the simulation calculation of the short-circuit arc impact process in the protection device is carried out. Taking the 220 kV spring contraction energy release method cable joint protection device as a calculation example，the area with the most concentrated stress inside the protective device is located at the end contraction, with a stress distortion rate of 24%, and the stress at the end contraction results in a safety margin value of only 4.09% for the device. It is considered that the key to improve the safety margin of the cable joint protection device is to reduce the stress distortion rate. A method of covering the inner stress concentration area of the cable joint protection device with ceramic silicon rubber polymer composite refractory material is proposed to improve the safety margin of the protection device. After calculation, a material with a thickness of 6 mm is selected to cover the inner stress concentration area, which can reduce the stress of the device. The distortion rate at the stress distortion point is reduced to 7%, and the safety margin value of the protection device is increased to 31.81%, increasing the overall safety margin of the protection device to 18.18%. Compared with the traditional improvement method, it is more targeted, promotes the development of lightweight equipment, and provides new solutions and methods for the safety design of 220kV high-voltage cable joints.