In order to solve the problem of low injection efficiency of p+n emitter junction caused by incomplete ionization of p-type SiC in bipolar SiC power devices at room temperature, our group proposed to use the heterojunction formed by wide bandgap p-type CuAlO2 and n-type SiC as the emitter junction. In this work, CuAlO2 thin films were prepared on 4H-SiC (0001) by sol-gel method. The influence of low heat treatment temperature range on the crystal structure, surface morphology and optical properties of CuAlO2 thin films were studied. The results show that the formation of intermediate product CuO can be enhanced at higher heat treatment temperature, promoting the generation of CuAlO2 phase in the solid phase reaction stage. The prepared CuAlO2 thin films are mainly oriented with the (012) crystal orientation of CuAlO2 phase with high crystal quality. In addition, the higher heat treatment in low temperature range is beneficial to obtain high quality CuAlO2 thin films with uniform surface and lower concentration of Cu-vacancy defect. The surfaces of the films are uniform with an average crystal grain size of approximately 35 nm when the heat treatment temperature in low temperature range is 300 ℃. The CuAlO2 thin films are highly transparent, with optical transmission exceeding 70% across the whole visible range. Meanwhile, the optical band gaps of the CuAlO2 thin films increases slightly with the increase of heat treatment temperatures in low temperature range.