Abstract: The nonlinear optics of the microsphere cavity at whispering-gallery mode(WGM) was analyzed. The resonance characteristics and the demodulation curve were simulated for SiO2 microsphere cavity, whose diameter was 1 mm. The testing system of coupled microsphere cavity with the taper fiber was set up. The full width at half maximum(FWHM) is 78.42 MHz, thus quality factor is 2.5106. The resonance characteristics and the demodulation curve derive from the experiments based on the sine wave phase modulation technique，which is free of pulse noise induced by phase reset. Loop frequency locking technique was used, then the resonance frequency was tracked and locked; and the locking precision and the locking time were analyzed. Experiments results show that the time for locking to 1% of the transmission intensity is 8 ms. The resolution of measured resonance shift is 375 kHz. Thus, it provides an experimental basis for sensing measurements of the microsphere cavity.