The present invention relates to a method for preparing a porous polymer film having a controlled pore depth, and a porous polymer film prepared thereby. A method for preparing a porous polymer film according to the present invention allows the pore depth of a porous film to be controlled simply and at a low cost, and thus allows adjustment of the light reflectance of the prepared film. A large-area film can be prepared by means of a simple method and thus can be applied to various industry fields. Films having different reflectance can be prepared and thus can be applied as low-reflection and high-reflection films for solar cells, and also as a low-reflection or high-reflection thin polymer film in the construction field or material and equipment field.