The invention relates to the technical field of industrial computer control, and provides a rejection testing method and device for a control system based on a redundant structure. The testing method comprises the steps of: determining the number N of redundant parts of the redundant structure of the control system and the number M of the fewest redundant parts to be output when the control system can be triggered to carry out an overall operation; determining a rejection probability passing index P of the control system, and acquiring a rejection probability passing index p which needs to be satisfied by each redundant part in the control system according to the index P; acquiring the smallest number n of tests according to the index p; testing one redundant part in the control system, and if the tested redundant part does not perform rejection after continuous n tests, determining that the rejection probability of the control system can meet the requirement of the index P. Therefore, the method and the device can shorten the test time, improve the credibility of test results and simplify the test process.