The present disclosure provides a method for preparing compound semiconductor sensitive film based on a displacement reaction-thermal oxidation method, the method comprising: growing a layer of Zn on a high temperature-resistant substrate; submerging the substrate on which the layer of Zn has been grown into ionic solution of soluble salt of Cu, such that Cu ions in the solution are displaced so as to separate Cu nano-particles out on a surface of the layer of Zn; and performing a thermal oxidation process on the layer of Zn to whose surface Cu nano-particles are adhered, such that the Cu nano-particles are oxidized into CuO nano-particles, so as to obtain a ZnO gas sensitive film that is doped with CuO nano-particles. The above preparing method has the following advantages: good filming quality, simplified preparation process, low cost and easy to control.