Soft X-ray multilayer coating is the one of studied hot points in applied and engineering optics. The reflectivity of multilayers is the most important parameter of multilayer coating performance and coating quality. The measurements of multilayer coatings is key to study the performance of coatings and improve the techniques of manufabrication. The relative reflectance measurements of some soft X-ray multilayers were completed successfully by splitting the spectrum of a laser-produced plasma source from a large area transmission grating spectrograph with a pre optics

+1 or -1 order spectrum was reflected by a multilayer. Another arrangement was that +1 order spectrum was reflected by one multilayer whose reflectance was known and -1 order spectrum was reflected by one multilayer whose reflectance was unknown. The SIOFM X-ray film made in China was used. The results of measurements show whether the quality of multilayers was good and provide some important basis for improving the technique of fabricating multilayers.