Solving the coupled Raman amplification is the main limitation to the efficiency of the existing optimization method for Raman fiber amplifier design. The least squares support vector regression model is applied to address this issue. Instead of directly calculating the Raman coupled equation, a multi-input multi-output model for Raman fiber amplifier is established. A C-band Raman fiber amplifier with a gain ripple level of ± 0.5 dB is designed using only two pumps. Additionally, the on-off gain can be quickly and directly adjusted by the proposed model. Compared with the shooting algorithm and average power analysis technique, the results indicate that the proposed regression model greatly improves the solving efficiency.