Memory fault simulator is an important tool for memory test sequence optimization. Traditionally, we use fault count to calculate fault coverage. However, it cannot represent accurately the real coupling fault distribution. In this paper, we adopt the concept of weighted coupling fault targeting DRAM.We propose a weighted fault coverage function with assigning weight parameters to coupling faults. With the weighted function, we can use physical information to calculate coupling fault coverage. Experimental result shows that the weight of intra-word coupling fault can be 10% to 14%; while the original fault count method cannot distinguish the degree of importance between different memory configurations.