Abstract: Abstract: Butanol is known as a typical second generation biofuel, and it has many advantages as an alternative fuel for engine. At present, the main studies about butanol concentrate on the combustion and emission characteristics. But the research on the spray characteristics is less. The spray atomization of fuel is a key factor that influences the combustion and emission characteristics of diesel engine. So it is important to research the spray characteristics of butanol and diesel blended fuel in depth. First conduct the spray visualization experiment on the spray test bench of high pressure common rail. Then according to the test results, this paper established nozzle flow model and spray model with the aid of AVL Fire software respectively. The nozzle flow and spray are regarded as an unified whole to research the spray characteristics of butanol and diesel fuel mix, and the calculation result of nozzle multiphase flow is used as the initial and boundary conditions for the spray simulation. Then the accuracy of the model is verified by the contrast of spray penetration and spray image. The influence of injection pressure, environment pressure and blending ratio on spray characteristic of n-butanol/diesel blends was studied by the model. And calculate the influence of various factors on the spray form development, spray penetration, SMD, velocity field and concentration field of blended fuel. In this paper, Nn indicates n-butanol and diesel blended fuel with the volume fraction of n-butanol is n. The results show that with the change of injection pressure and environment pressure, the spray form of blended fuel N25 remain unchanged basically. And the differences of spray form mainly displays in the spray penetration and spray cone angle. With the increase of injection pressure, the spray penetration of N25 increases gradually, and sauter mean diameter (SMD) decreases gradually. Then select two points in the velocity field. By comparing the speed of the two points, it can be seen that the speeds of the two points all increase with the increase of injection pressure. This can indicate that the air entrainment enhances with the raise of injection pressure. And the spray center speed and concentration near the axis all increase, with the increase of injection pressure. According to the results of the research on back pressure, with the increase of environment back pressure, the initial velocity of droplet decreases and resistance increases, so the spray penetration of N25 reduces. And SMD is basically unchanged in middle and later of the spray. Because initial velocity of droplet is reduced, which is not beneficial for the droplet broken. Meanwhile with the increase of backpressure, environment density increase, the interaction of environment and fuel enhance, which make the droplet broken quickly. The spray center speed reduces, concentration near the axis increases. According to the results of the research on blending ratio, with the increase of n-butanol blending ratio, the viscosity and surface tension all decrease, then the droplets is easily broken, which leads to the spray penetration and SMD all reduce, and the atomization becomes better. With the increase of environment temperature, the spray penetration of N25 reduces, and SMD significantly decreases after temperature increased by 293.15 K. And then there is a little change with the temperature increasing. In this paper, the spray model is much closer to the actual situation because of coupling the flow inside the nozzle. This paper researches and analyzes the influence of various factors on spray macroscopic and microscopic characteristics of butanol and diesel blended fuel. So this paper could provide a theoretical support for the application of butanol as an alternative fuel for engine.