Abstract: High intensity electromagnetic interference will be induced during the operation of the " Dragon-Ⅱ" linear induction accelerator, which will interfere the operation of the key equipments such as the constant current supply. The characteristics of the interference signal was analyzed throughly. Then the high reliability circuit for the constant-current supply was designed based on the comprehensive application of several techniques, such as the digital fiber communication system and the dual loops current and voltage feedback control system. Combined with the application of the common mode inductor, the isolation ground and the optical-electronically isolation module, the electromagnetic compatibility of the HL90 constant-current supply was improved greatly. The low ripple high current HL90 worked well in the high intensity interference circumstance. The coefficient of the ripple was less than 0.11%, the drift was less than 0.12% and the malfunction percentage was less than 0.01%. This is helpful for the success of the "Dragon-Ⅱ" LIA.