It is the key content of laser warning to reliably and real-time detect the type and characteristic parameters of incident laser.Coherent detection technology detects the information based on the coherence of laser,and is a kind of effective detection technology.In order to detect the incident laser’s spectrum,a kind of device for laser detecting and real time spectrum measurement was designed,which measures the laser spectrum on the bases of coherent detecting technology,Fourier optics and optical signal processing.Using compact and static Mach-Zehnder interferometer as the coherent detection components,it can restrain the background light efficiently.The non-scanning mechanical parts allow fast spectrum detection,and narrow laser pulse can be detected.The real-time signal processing is realized by DSP and multi-channel frame subtraction technology to wipe off the background light,detect the laser and measure its spectrum.The result indicates that,using Mach-Zehnder interferometer and multi-channel frame subtraction technology can realize the laser pulse detection,and improve the measuring precision efficiently;10 ns laser pulse can be detected and the wavelength measuring error is less than 10 nm.