An optical engine of the mini-projector suitable for the personal use is designed. It is a single panel digital light processor (DLP) system by using LED as its illuminator and X prism as its mix-color device, which can provide a 38.1～50.8 cm color projection display. The theoretical analysis shows that the design can satisfy the need of the color projection display with the system efficiency 16.1%. The simulation by using the software is LightTools made. After three million rays are traced, it shows that the efficiency of the optical engine is 14.6% with flux 22.8 lm on the screen. The simulation results coincide with the theoretical analysis of the system efficiency. The ANSI nine-point uniformity of the screen is 91.55%, -93.36%, which can reach the specification of the design.