In mixed criticality systems, tasks with different criticality levels share a common platform, which makes the schedulability more complex. Considering AMC (adaptive mixed criticality) scheduling is currently the most effective fixed priority approach for scheduling mixed criticality systems, this work presents a response time analysis algorithm AMC-PM (AMC partition max) for AMC. In AMC-PM, the WCET (worst case execution time) of the task is partitioned into low critical execution time and high critical execution time. Then an upper bound of response time can be derived by adding the response times of the two parts together. For tasks with small WCET, evaluations illustrate that AMC-PM can significantly enhance the schedulability comparing with AMC-rtb and that AMC-PM can effectively decrease the run time comparing with AMC-max.