Since both the measuring range and the resolution of a traditional grating interferometer were difficult to be improved simultaneously,a grating interferometry based on a single long metrology grating was presented.Firstly,an interferogram was generated by interference between the ±5 orders beams diffracted by the grating.The length of the grating was 400mm and its pitch was 10μm.The optical fringe multiplication achieved was 10.Then,a fringes subdividing method based on the time-shift property of Fast Fourier Transform (FFT) algorithm was developed.By calculating the phase change of the fringes at a certain position between two sequential acquisition interferogram,the fringes were subdivided electronically and the subdividing multiple was as high as 1000.During this course,the effect of energy leakage on the phase-extraction precision of FFT was suppressed by tailoring the acquisition interferogram into a few full-multiples of the fringes.The resulting subdividing precision could reach at least 1/1000 period of the fringes.Simulation and experimental results show the system resolution is 1nm and measurement precision is less than 10nm.