Diamond NV color-centered quantum sensor has advantages of high sensitivity, high accuracy and operational stability in partial discharge detection, but the spatial layout of sensor will affect its measurement performance, so it is necessary to explore its optimal measurement position. This paper establishes the discharge model of cable body and intermediate joint firstly, simulates the electromagnetic wave propagation characteristics of the discharge model secondly, and investigates the attenuation characteristics of the electromagnetic signals at different detection points finally to obtain the magnetic flux density and analyze the optimal layout of the sensor. The results show that when partial discharge occurs in the cable, the electromagnetic wave signals propagate and decay rapidly, and the attenuation of the electromagnetic wave signals outside the metal shielding layer is worsened due to the existence of the metal shielding layer inside the cable, where magnetic flux density is only at the pT level with 99% attenuation. Therefore, combining with the measurement range of the diamond NV color-centered quantum sensor, the sensor can be placed in the filler layer in cable body and placed in the sandwich between the copper mesh and the sealing layer in cable joint.