The wave configuration of a double Mach reflection (DMR) with a convexly curved Mach stem and the resulted flow fields are analyzed. An analytical model describing the formation of a DMR with a curved Mach stem and predicting its wave configuration is proposed. The transition criterion from a DMR with a straight Mach stem to a DMR with a curved Mach stem is also suggested. Predictions based on the analytical model are compared to experimental results. The agreement is found to be good to excellent.