Diffraction grating is widely used in a variety of applications, which requires the grating to have good quality. Among various methods of making large-sized gratings, laser direct writing has obvious advantages. We use the parallel direct laser writing technology to produce a sinusoidal grating with size of 100 mm×100 mm and line number of 1780 line/mm. Firstly, the grating is analyzed theoretically to find a groove depth where the sinusoidal grating can reach its highest efficiency, then the grating is produced by laser direct writing and finally coated with a layer of gold. We introduce the diffraction efficiency measurement of the grating, and estimate the uniformity of the grating. The result shows that the diffraction efficiencies of the grating are around 90%, which is close to the theoretical calculation. Meanwhile, the efficiency distribution is uniform. Experimental results demonstrate that the developed parallel direct laser writing technology is feasible for producing high quality and large-sized gratings.