As a class of rateless erasure codes, Luby transform (LT) codes are successfully applied to the reliable data transmission in wireless communication. Degree distribution is critical to the performance of LT codes. However, the classical Robust Soliton Distribution (RSD) is not suitable for short-length LT codes. To solve the problem, a method is proposed to optimize the degree distribution for LT codes over Binary Erasure Channel (BEC). Based on the properties of degree distribution, the Artificial Fish Swarm Algorithm (AFSA) is used to optimize the proportions of some important degrees in RSD. Simulation results show that compared to other optimized degree distributions and RSD, the new degree distribution reduces the overhead, and saves the average consuming time per encoding/decoding process.