The energy from the source was rearranged through the reflection by a freeform reflector, and the desired illumination on a certain plane was got, which simplified the illumination system in the projectors and provided a choice to minimize the device further. A partial differential equations set was presented according to the character of the light source and the desired energy distribution on the illumination plane. The numerical results of the partial differential equations set were investigated to obtain a freeform reflector. LED with a Lambertian light emitting surface of 1 mm×1 mm and a viewing angle of 120° was applied as the light source, and the desired illumination on certain face was a 4∶3 rectangular. Two kinds of free reflectors were designed, and the simulated results showed a uniform illumination near to 90%. The projection lengths on the optical axis of both free form reflectors are less than 25 mm, and the projection lengths on the axis perpendicular to the optical axis are both less than 22 mm. The total lengths of the illumination system are both less than 40 mm, so this system is very compact and suitable for the portable LED projectors.