Based on the rigorous coupled-wave analysis, the optimized design for a transmission two-gratings mask for 13.4nm soft X-ray interference lithography has been accomplished. Then a large area transmission gratings was successfully fabricated by electron beam lithography (EBL), which has an area of 1.5mm×1.5mm, ruling period of 100nm, Cr relief thickness of 50nm, gap/period of 0.6, and Si3N4 substrate thickness of 100nm. Based on the quantitative estimation of the measurement data, the first and second order diffraction efficiencies were determined as 4.41% and 0.49%, respectively， in good agreement with the numerical simulation results. Through comparison between the measurement and the numerical simulation results, it was shown that the relief is entirely vertical and the gap/period was well controlled. This two-grating mask will be used installed on the soft X-ray interference lithography endstation at Shanghai Synchrotron Radiation Facility (SSRF). With its 1st and 2nd order diffraction, 50nm period and 25nm period gratings can be cost-effectively fabricated, respectively.