This paper introduces a method of on-line measuring center wavelength in photolghographic excimer laser using echelle and Fabry-Perot (F- P) etalon which have small dimension and low cost(compared with traditional spectrometer),under the condition of high repetition rate of 500－3000Hz.Through the analysis of the F-P etalon interference fringes and grating diffraction line fringes,after a series of algorithms to deal with data,finally is high measuring accuracy of sub-picometer realized.The stan dard deviation of the center wavelength measurement results is lower than 0.1pm,and good experimental results are obta inedand.