Abstract: The dielectric wall linear accelerator, based on technologies of solid-state pulse forming lines, photoconductive semiconductor switches and high gradient insulators, is a new concept linear accelerator being developed at Institute of Fluid Physics, CAEP. During accelerator test process, the measured energy gain of the accelerated proton beam is much lower than expected. After the exclusion of the pulsed power source factor, we find that the coupling effect induced connecting circuit is the main factor of causing low beam energy gain. Based on discharge circuit analysis of the dielectric wall linear accelerator acceleration unit, we confirm that the circuit coupling between acceleration units is inevitable. The circuit coupling of several different operation modes is studied by measuring the circuit current. According to the characteristics of the coupled circuit, we give two kind of decoupling methods based on the magnetic core isolation, and we measure the efficiency of the decoupling of the two methods.