The present invention provides a cable joint partial discharge built-in capacitive sensor optimization design method. The method comprises the steps of: determining a cable joint built-in capacitive sensor equivalent circuit model and related circuit parameter information, and constructing a corresponding circuit simulation calculation model according to the equivalent model and the related circuit parameter information; for the equivalent stray capacitance between the corresponding ring electrode and a flange, the parallel damping resistance between the ring electrode and the flange and the equivalent stray inductance of a metal connection line between the ring electrode and the cable joint, changing parameters of the three; calculating the circuit model to respectively obtain the influence laws of the three for the sensor checking performances, establishing a cable joint built-in sensor integrated undistorted model to calculate and obtain a corresponding relation of the size and thelocation of the sensor and the parameters of the three, and determining the optimization design scheme of the sensor. The cable joint partial discharge built-in capacitive sensor optimization design method optimizes the structure design of the sensor and the built-in location of the sensor in the cable joint so as to achieve the purpose of improving the cable joint partial discharge signal detection capacity.