Abstract: The turbine blade is a critical component of waterpower generator. In order to real time detect the cracks of blade fast and exactly and to avoid accidents and decrease losses, an optical fiber Michelson interferometer is designed based on interference principle of light. The sizes of signal arm and reference arm are determined. The experimental device of optical fiber Michelson laser ultrasound is established for detecting the crack of turbine blade. The experimental results show this sensor machine simply and have low cost. It can detect the crack of blade efficiently and fast. The results offer the experimental basis for studying the law of cracks expansion.