An improved memory system simulator based on DRAMSim2 is presented. The memory system simulator has been widely used in the design space exploration of the SoC (System on Chip). DRAMSim2 is one of the more common DDR2/3 memory system simulators. A memory system consists of the memory controller and the DRAM device. DRAMSim2 models the memory controller in a general way, which makes it impractical to faithfully track the behavior of a specific memory controller. In this work, we present an improved memory system simulator based on DRAMSim2. In response to the differences between the memory controller DRAMSim2 modeled and the practical controller, part of DRAMSim2 is modified and improved, considering the structure characterizations of the practical controller. Experiments show that the improved simulator properly matches the practical memory system.