Based on the Fluent software, a two-dimensional calculation model of a direct injection diesel rotary engine coupled with a reduced reaction mechanism of n-heptane was established. The reliability of the model was verified by literature data. For the unchanged injection duration, the influence of single injection timing and second injection timing on the combustion process was compared and studied. The results show that the cylinder pressure and the cylinder temperature increase with the injection timing delay. The CO generation was higher and the NO generation was lowest when the injection advance angle was 40 °CA. When the pre-injection timing was -40 °CA and the main injection timing was –8 °CA, a high in-cylinder pressure was maintained, and the CO generation was reduced by more than 25% and the NO generation was increased compared to the single injection timing of — 40 °CA.