The main operations of elliptic curve cryptosystems (ECCs) are scalar multiplications and multi-scalar multiplications, which heavily determined the overall implementation of the efficiency of ECC. This algorithm extends the fixed-base window method by using the signed integer factorial expansions of scalar. The main characteristic of this method is that only a point addition computation is required, and it greatly improves the computational performance of a multi-scalar. Furthermore, the correctness proof and complexity analysis of the new algorithm are presented. At last, experimental results show that the computational efficiency increases about 47.8% to 56.5% when compared with other existing methods in the case m=2.