In the face of the pressure of global warming, the use of carbon-free fuels in internal combustion engines to reduce emissions has received extensive attention. In order to study the effects of diesel injection strategy on combustion and emission characteristics of ammonia-diesel dual fuel engines. Caterpillar 3401 diesel engine was taken as the research object, a simulation model was established with CONVERGE software to study the effects of different injection rate profiles (trapezoid, wedge, slope, triangle and rectangle) on combustion and emissions characteristics of ammonia/diesel dual-fuel engine under the conditions of 40% ammonia energy fraction, the same fuel injection volume and fuel injection duration. The results show that the diesel injection rate profile has a significant effect on the mixture of diesel, ammonia and air, thus affecting combustion and emissions. When the injection rate profile is trapezoid, the injection rate is higher in the injection stage and the mixing time of ammonia and diesel is longer, which makes the ammonia-diesel mixture more uniform, and the corresponding unburned ammonia emissions is lowest. Compared with the rectangle injection rate profile, the indicated mean effective pressure of the trapezoidal, wedge, slope and triangle injection rate profiles increases by 4.36%, 0.76%, 1.09% and 3.08%, respectively. Due to the small difference in maximum temperature, which results in very little variation in nitrogen oxides for each injection rate profiles. A scheme of injection rate profile for improving combustion and emissions performance of ammonia-diesel dual fuel engine is presented.