This paper analyzes and compares various carrier sequences generated by the mathematical formula and pseudo random binary sequence (PRBS) of random frequency pulse width modulation (RFPWM) tables. RFPWM techniques for inverter-fed motor can improve the harmonic spectrum of the output voltage, the emitted acoustic noise and the mechanical vibration. From our analysis, we can find that the different RFPWM carrier table with the same carrier frequencies may results in the different voltage spectrum. In this paper, the optimal carrier sequence is found through the proposed index with the help of the personal computer. The result also indicates that we should put more attentions on the carrier sequences than that on the selection of carrier frequency.