The invention relates to a process for preparing a stretchable supercapacitor based on a highly conductive graphene/nickel particle mixed structure. Firstly, a chemical vapor deposition method is used for preparing spongy graphene material on a nickel foam, and the prepared graphene/nickel foam are immersed in an etching solution for slow reaction so that most of the nickel metal can be chemically displaced into various small nickel particles; secondly, the spongy graphene/nickel particle mixed structure is fished out from the etching solution by using a seal-type fishing method, cleaned and dried, and a pre-stretched elastic substrate slowly returns back to the original length or area; and thirdly, the prepared stretchable graphene/nickel particle mixed structure is used as electrode material, and an all-solid-state stretchable supercapacitor is prepared according to the elastomer/electrode/solid electrolyte/electrode/elastomer structure. According to the invention, the capacitance of a conventional capacitor is increased, contact resistance is reduced, the stretching stability, frequency and performance are excellent, the cost is low, and the method is controllable and suitable for mass production.