In one exemplary embodiment, a three dimensional printing system may include a tank filled with liquid forming material, a carrier platform, an optical module disposed under the tank, and a control module is provided. The control module is electrically connected to the optical module and the carrier platform, such that the carrier platform is controlled to move in the tank, and the optical module is controlled to generate light irradiating to the liquid forming material to form a solidification layer on the carrier platform. An image position of the optical module is located in a specific position away from the bottom of the tank in the liquid forming material to form a solidification plane, the liquid forming material at the solidification plane is cured and solidified to form the solidification layer, and a plurality of solidification layers are stacked to form a three dimensional object.