A three-dimensional printing apparatus including a tank, a moving platform, a light source disposed below the tank, a detecting unit and a control unit is provided. The tank is filled with a liquid forming material and a separating liquid, wherein the specific density of the separating liquid is larger than the specific density of the liquid forming material, so that the separating liquid sinks between the tank and the liquid forming material. The control unit controls an initial depth at which the moving platform immerses into the liquid forming material, so as to form a three-dimensional object. A three-dimensional printing apparatus is also provided, wherein the light source thereof is disposed above the tank, and the specific density of the liquid forming material is larger than the specific density of the separating liquid, so that the liquid forming material sinks between the tank and the separating liquid.