The classic Raman coupled equations, which describe the principles of the interaction between the incident and generated laser, have important applications in numerous domains. However, the classic Raman equations ignored the off-axis generated laser energy, which cannot be ignored in certain circumstances. We improved the classic equations by considering the off-axis laser energy of the stimulated Raman scattering. A single-pass multiwavelength potassium gadolinium tungstate crystal Raman generator pumped by a picosecond Nd:YAG laser was realized. On the basis of theoretical calculation and experimental verification, the improved equations produced numerical results for the output spectrum and output laser conversion efficiency that have a better agreement with the experimental results than the classic equations.