A new laser interferometric system with nanometric accuracy is developed.Optical system with 8 times optical path difference is designed.The following materials and methods are utilized:simple

stable and compact optical layout;coupled defferential interferometry;symmetrical optical paths;multiplication optical path difference;Abbe principle.The accuracy of the system is analyzed and the result is about ±1.8nm within the range of 10mm.The test is given by comparing with the capacitive micrometer.Experiment results show that the measuring accuracy is about 14nm.