A nondestructive laser detection method is proposed by combining the spatial laser injection into fibers with the coherent detection technique. The transmission characteristics of laser ultrasonic signals and the principle of coherent light detection are analyzed, and the signal processing and noise suppression methods in the nondestructive laser detection are discussed. The experimental system is established based on the laser excitation and detection where the laser injection and polarization-maintaining transmission are the cores, and the human-machine interactive system based on the graphical programming language LabVIEW is the monitoring way. The experimental results show that this system can reduce the influence of background light jitter on signal detection. By controlling the spot diameter and energy, one can obtain the reflection peaks of different ultrasonic signals. The sensitivity and smoothness of the ultrasonic echo signal detection on material defects are improved effectively. The testing method provides a new technique for engineering applications.