Remote Direct Memory Access (RDMA) is widely deployed in Data Center Networks (DCNs), but it is sensitive to packet loss due to the Go-Back-N retransmission. Forward Error Correction (FEC) can mitigate this issue by introducing redundancy to recover lost packets. However, the fixed coding parameters of FEC hinder its adaptability to dynamic network conditions, leading to inefficiencies and unreliability. To address this issue, we propose DCTS-RDMA, a dynamic coding transmission system for RDMA. DCTS-RDMA incorporates a monitor to detect packet loss in real time and a Dynamic Coding Packet (DCP) algorithm to adaptively adjust the coding group size and redundancy based on the detected loss, thereby overcoming the inefficiency of fixed coding parameters. To support varying coding decisions, the selected parameters are transmitted to an encoder at the sender to generate redundant packets, while a decoder at the receiver reconstructs lost data using both the original and redundant packets. We implement DCTS-RDMA using C++/HLS on an FPGA-based simulation platform and conduct extensive experiments. Under low packet loss conditions (less than 1%), our DCTS-RDMA reduces redundant overhead by approximately 85% and decreases total execution time by 7.5% compared to fixed coding strategies.