The diffraction efficiency of a gold transmission phase grating is simulated as a function of the depth of grooves and the duty cycle on the basis of the scalar diffraction theories. It is shown that the +1 order diffraction efficiency of a transmission phase grating with appropriate groove depth and duty cycle can beup to 21.9% of the incident light，whereas it is no greater than 10% for a conventional amplitude-mode transmission grating. Transmission gratings with area of 20mm×5mm，period of 1μm，duty cycle of 0.55 and 200nm thick gold bars supported by a membrane of 300nm thick polyimide have been fabricated by combining holographic lithography and electroplating. Its diffraction efficiency has been measured in national synchrotron radiation laboratory，and the maximum efficiency in +1 order is about 16% at λ=7.425nm.