Abstract: An improved broadband coupled normal wave model is proposed to address the issue of low computational efficiency in pulse propagation through horizontally varying waveguides. The phase function expression satisfied by normal mode eigenvalues is combined with the global matrix-coupled normal wave model in this method. The frequency and depth are extracted by transforming the phase function. By reducing the four-dimensional root searching of frequency, depth and real and imaginary parts of the eigenvalues to a two-dimensional root searching of only the real and imaginary parts, the calculation efficiency of local normal wave eigenvalues in horizontally varying waveguides is significantly enhanced. As a result, this improved broadband coupled normal wave propagation model achieves higher computational efficiency while maintaining accuracy. Numerical simulation is conducted on broadband sound field in a horizontally varying sea waveguides, demonstrating that when dividing the seabed into 40 or more, this proposed model exhibits 5.9 times higher computational efficiency compared to COUPLE07 model without compromising accuracy.