Abstract: Aims to analyzing indoor sunlight distribution and solar radiation heat gain of wing-room in Huizhou traditional dwelling, and with Ecotect software, the effects of building orientation and depth-width ratio of dooryard on the solar radiation heat gain of wing-room were simulated and compared. Results show that the sunlight hours are less than 1 h for more than 80% of indoor areas, and the sunlight can enhance passive evaporative cooling of water under the dooryard which enhances indoor natural ventilation during the night. These are the main reasons for the cool interior of traditional dwellings during the summer. In winter, 15% of hight sunlight hours region is mainly located in the wing-room and living-room, which reduces the room heating load and provides a heathy as well as hygienic indoor environment. It is also demonstrated that the solar radiation heat gain of the wing-room can achieve the maximum when the building is facing towards South. And the solar radiation heat gain will be enhanced by increasing the depth-width ratio of dooryard. Under an optimal building orientation and dooryard size, approximately 14.7% of building heating demand can be satisfied by the solar radiation heat gain in winter.