The spray process of diesel rotary engine was studied by means of constant volume bomb, schlieren device and high speed camera. The influences of back pressure and spray pressure on spray characteristics were emphatically analyzed. The results show that the spray diffusion rate increases rapidly and then decreases step by step during the spray process. The spray cone angle decreases sharply in the initial atomization stage and remains relatively stable in the stage of secondary atomization. The increase of spray environment pressure effectively shortens the spray penetration distance and increases the spray cone angle, which provides the test data for the optimization of fuel injection timing. With the increase of injection pressure, the spray penetration distance and spray cone angle increase and the initial fuel atomization and secondary atomization hence improve, which is beneficial to improve the spray quality of rotary engine. Accordingly, the mixing state of fuel and gas for rotary engine can be improved.