Conventionally, many researchers and experts are only focused on studies of Routing Protocol over the MANET. Currently, the pervasion of Internet applications causes TCP as the standard transmission protocol for most of the networking applications. For the reliable packets delivery, TCP can support the mechanisms of flow and congestion control. Due to the unconstrained movement of the mobile nodes, TCP is unable to notice network congestion or link down to activate related controls on the MANET. Hence, the main purposes of this paper are to refine the influence parameters and to establish their setting rules for TCP performance on the MANET. First, we discuss several TCP parameters, which affect the performance. According to these parameters, we can statically adjust related RTO parameters and analyze Congestion Window in congestion control for evaluating the performance through the simulation on the MANET. Also, we did propose the tuning rules to improve the TCP performance based on simulation results. Consequently, the final result of this paper can be the reference for further studies in QoS features and other applications on the MANET.