Abstract: Model-based diagnosis has been popular in the field of artificial intelligence. In recent years, with a gradual increase of the efficiency of SAT solvers, model-based diagnosis is converted into SAT problem. After deeply studying CSSE-tree algorithm—a method for solving model-based diagnosis, combining with the characteristics of diagnose problem and SAT solving process, we solve the problem by diagnosing the candidate solutions which contain more elements first, thereby reducing the scale of SAT problem. Based on the minimal diagnostic solutions and non-minimal pruning methods on diagnostic solutions, we firstly propose a non-diagnostic solution theorem and a non-solution space pruning algorithm, which implements the non-solution space pruning effectively. We first solve the candidate solutions which contain more elements. According to the features of solution and non-solution method, we construct LLBRS-tree method based on reverse search. Experimental results show that compared with the algorithm of CSSE-tree, the algorithm of LLBRS-tree has less number of SAT solving, has smaller scale of the problem, better efficiency, especially when solving multiple diagnose problems its efficiency is more significant.