Homogeneous charge compression ignition (HCCI) is a new combustion concept, which achieves high thermal efficiency and ultra-low emissions. In order to realize the HCCI combustion, a homogenous mixture preparation plays an important role in the HCCI engine concept. However, there are some problems for conventional diesel fuel to achieve a uniform mixture distribution in the cylinder because of its high viscosity and low volatility. This paper describes the effects of the DME addition on the spray behavior and atomization characteristics of diesel fuel. Pure diesel fuel, pure DME fuel and DME/diesel blended fuels with DME mass fraction of 25% and 50% were used to evaluate the effects of the DME concentration on the macroscopic and microscopic structure of the steady spray. The macroscopic structure of the spray, such as the spray pattern and spray cone angle were recorded by a digital camera at the nozzle tip, and microscopic structure of the spray, such as droplet size distribution and sauter mean diameter (SMD) were measured by a laser size analyzer (LSA). The experimental results reveal that the DME concentration in the DME/diesel blended fuels had significant influence on both the macroscopic and microscopic of the spray due to the micro explosion and flash boiling function. The spray cone angle of blended fuel was increased with the increase of DME concentration. At the centerline of the spray, the SMD decreased with the increase of the DME concentration, and it decreased rapidly near the nozzle tip. On the other hand, it can be seen that more small droplets are distributed for DME/diesel blended fuels than that for pure diesel fuel. From the results, it can be concluded that it is a novel way to use DME addition into diesel fuel to enhance the fuel/air mixture formation.