Rayleigh Brillouin optical time domain analysis system can be operated with single laser and single end of sensing fiber in a non-destructive way, and the modulation of pulse base and pulse with an intensity-type electro-optic modulator is the key technique for obtaining continuous light and pulse light required by the system. A new modulation method with a pulse applied to the bias port of electro-optic modulator and a microwave applied to the RF port of the electro-optic modulator to modulate the pulse base and pulse is analyzed theoretically, simulated with computer and studied experimentally in this paper, and the optimal operating point of electro-optic modulator in Rayleigh Brillouin optical time domain analysis system is discussed. The results show that if the operating point of electro-optic modulator is set at the valley and peak of its transmission curve respectively and the amplitude of microwave modulation signal is chosen appropriately according to the configuration and performance of the actual system, then the continuous light and pulse light meeting the requirements of Rayleigh Brillouin optical time domain analysis system can be obtained when the pulse base and pulse are to be modulated. The results of this study can provide a theoretical basis for the optimal design of Rayleigh Brillouin optical time domain analysis system.