To be used in sound sensor field, a new intensity modulated optic microphone theory is introduced. Here single-mode optical fiber and single fiber C-lens are used to realize light intensity modulation; the system also contains micro-electro-mechanical system (MEMS) membrane to be compatible with vibration displacement. Simulation results show that the proper choice of parameters like membrane size can make the sensitivity of sensor improve in orders of magnitude than traditional light intensity modulation methods, and the experimental results also show that the theoretical simulation is persuasive.