The invention discloses a sunlight transmission system for a building. The sunlight transmission system includes a dual-axis attitude control mechanism, a controller, a light position sensor and optical components, wherein the optical components include a movable optical component and a fixedly-installed optical component; the movable optical component includes an optical daylighting device; and the fixedly-installed optical component includes a one-level receiver and follow-up receivers. The system converges incident sunlight and economically and accurately transmits the light into the building in an approximate parallel light form without relying media such as optic fibers. Tracking the sun, the system converts direct sunlight which is obliquely projected to the surface of the building into light transmitted along a fixed direction through reflection, and guides the light to enter the building through a multi-level reflection mechanism. The system can be directly installed at the facade of any building. The system is wide in application range, economical, simple and convenient; and the manufacturing cost and application cost of the sunlight transmission system can be greatly reduced.