An inkjet printing apparatus and a method of making gratings are provided. The inkjet printing apparatus comprises a base; a platform provided on the base configured to carry a substrate to be processed to linearly move in a first direction on the surface of the base; and a printhead assembly provided above the platform, wherein the printhead assembly includes a printhead support and a plurality of printheads provided on a side of the printhead support facing the platform, each of the plurality of printheads is provided with a nozzle, and the printhead assembly can move linearly in the first direction. The present invention is adaptable to using inkjet printing technology to make gratings.