Weighted Laguerre polynomials-finite difference time domain (WLP-FDTD) method is employed to analyze transient response of transmission line in high-speed interconnect circuit system. Based on telegraph equation in equivalent circuit networks model,current and voltage are computed with weighted Laguerre polynomials. According to orthogonality,stability condition is eliminated. Different from finite difference time domain method,WLP-FDTD method is unconditional stable,which separates time and space variables. It is fast in computing large number of dissection networks for a transmission line. It shows that WLP-FDTD method is more efficient than traditional FDTD in analysis of transmission line. At last,a program with GUI is developed.