Presented in this paper is an improved method for dealing with a mixing plane that exists between computational domains of two adjacent blade rows of a multiple-blade-row turbomachine. The method makes use of the semidiscrete flow equation updating scheme to convert flux differences across an interrow interface to conservative flow variable incrementals then to characteristic variable perturbations. Therefore, the proposed method bears more physics and is much more robust than any known method of its kind. As a result, reverse flow can be accommodated by this method naturally without any special treatment. Two existing methods are also included to provide a clear illustration of the differences and advantages of the new method. Two numerical test cases using a transonic compressor stage are presented to investigate the robustness of the new method and its influence on solution convergence, accuracy, and time cost in comparison with the two existing methods.