An algorithm for the verification of strong open bisimulation in π-calculus with mismatch was presented, which is based on the symbolic transition graph (STG). Given two processes, we can convert them into two STGs by a set of rules at first. Next, the algorithm computes a predicate equation system (PES) from the STGs. This is the key step of the whole algorithm. Finally, the PES is solved and the greatest symbolic solution is got. Correctness of the algorithm is proved and time complexity discussed. It is shown that the worst-case time complexity is exponential.