The development of science and technology need to calibrate the certainty of nanometer measurement instruments.A method is proposed to calibrate the nano fringe width of the dual frequency high-order weak feedback displacement measuring system based on Fabry-Parot cavity.By using the microcontroller MSP430F149,which can measure the ratio of frequency between high-order feedback nano fringe and the traditional weak feedback half wavelength fringe when adding a same displacement on the two target mirrors.As a result,the optical resolution of nanometer displacement measuring system can be calibrated accurately.The measurement results show that optical resolution of the system can be 10.37 nm,which is traceable to light wavelength.By adding 20 times electrical subdivision,the final resolution of this system is about 0.53 nm.