The invention relates to an optical engine for laser projection display of a three-piece liquid crystal on silicon (LCOS). The optical engine comprises a red laser, a green laser, a blue laser, three dodging and reshaping systems, an optical core, a three-piece LCOS, a reflecting mirror and a projection objective, wherein the luminescence centers of the three lasers are positioned on the main optical axes of corresponding dodging and reshaping systems; the three optical axes of corresponding dodging and reshaping systems are parallel with one another; three light beams emitted by the three lasers are adjusted into uniform rectangular parallel light beams by the dodging and reshaping systems respectively; two beams of light directly enter corresponding polarization beam splitters, and the other beam of light is reflected by the reflecting mirror and enters a corresponding polarization beam splitter; and polarized light in three colors is finally combined into white light and enters the projection objective by the optical core. The lasers are taken as light sources, generated laser light is small-bandwidth linear polarized light, and a color filter is not used, so that a large number of polaroids are eliminated, cost is lowered, and the utilization ratio of optical energy is increased simultaneously; and the color gamut range, color brightness degree and color fidelity degree of the optical engine are better than those of the optical engine of the conventional optical system.