In the big data era, data-intensive applications have growing demand for the capacity of DRAM main memory, but the frequent DRAM refresh, high leakage power, and high unit cost bring serious design issues on scaling up DRAM capacity. To address this issue, NVDIMM, which is a hybrid memory module, becomes a possible alternative to replace DRAM as main memory in some data-intensive applications. NVDIMM that consists of a small-sized high-speed DRAM and a large-sized low-cost non-volatile memory (i.e., flash memory) has the serious performance issue on accessing data stored in the flash memory because of the huge performance gap between DRAM and flash memory. However, there is no or limited room to adopt a complex caching algorithm for using DRAM as the cache of flash memory in NVDIMM main memory because a complex caching algorithm itself would already cause too much performance degradation on handling each request to NVDIMM main memory. In this paper, we present a light-weight data separation design to boost NVDIMM performance with limited data separation overhead for reducing the data accesses to flash memory. A series of experiments was conducted based on popular benchmarks, and the results demonstrate that the proposed design can effectively improve the performance of NVDIMM main memory.