Conformance checking refers to the alignment between a computational process model and its actual execution. Conformance checking at runtime has become a new problem in current conformance checking due to the real-time feedback and positive application prospects. For each newly generated event, how to calculate and obtain the optimal conformance checking at a low performance cost is a difficult point for conformance checking at runtime. Based on the refined process structure tree (RPST) of the process model, this study proposes a conformance monitoring tree (CMT) and a dynamic programming algorithm to obtain the optimal conformance result based on the CMT. Through three experimental datasets, it is shown that compared with the existing work, the proposed algorithm has obvious performance advantages.