The blade vibration monitoring method and system uses dual-channel time difference sampling method for two-way sampling signals, the vibration frequency of blade is measured by interpolation search, and the on line real time vibration frequency and amplitude monitoring is achieved. The system is comprised of three channels of optical fiber sensors, amplifiers, data collecting interface board and computer processing system, in which two channels of optical fiber sensors are installed with a definite interval on a circumference with same rotary plane of the blade.