This paper describes a mixed mode circuit simulation by the direct and relaxation-based methods with dynamic network partitioning. For the efficient circuit simulation by the direct method, the algorithms with circuit partitioning and latency technique have been studied. Recently, the hierarchical decomposition and latency and their validities have been researched. Network tearing techniques enable independent analysis of each subnetwork except for the local datum nodes. Therefore, if the local datum nodes are also torn, each subnetwork is separated entirely. Since the network separation is based on relaxation approach, the implementation of the separation technique in the circuit simulation by the direct method corresponds to performing the mixed mode simulation by the direct and relaxation-based methods. In this paper, a dynamic "network separation" technique based on the tightness of the coupling between subnetworks is suggested. Then, by the introduction of dynamic network separation into the simulator SPLIT with hierarchical decomposition and latency, the mixed mode circuit simulator, which selects the direct method or the relaxation method and determines the block size of the latent circuit dynamically and suitably, is constructed.