The invention provides a redundant DCS system and a redundant DCS system nuclear grade CPU load reducing method. The redundant DCS system comprises at least two DCS systems which are connected in a communication way. Each DCS system comprises a CPU system which is used for performing periodic data processing. The periodic data processing includes redundant system data tracking, and time occupied by redundant system data tracking does not belong to DCS machine cabinet response time. The method comprises the steps that S1, tracking content stored in the CPU system is changed according to the redundant mode of the DCS system and the actual use condition of the IO module of the DCS system; and S2, redundant system data tracking is performed based on the changed tracking content so as to reduce CPU resource occupied by the redundant system data tracking. Redundant system data tracking is improved so that the CPU resource occupied by the redundant system data tracking can be reduced, CPU load reserve percentage can be guaranteed, and increasing of DCS response time can be avoided.