In this paper, CdGa2O4 nanosheets were prepared by microwave-calcination method. CdGa2O4 nanosheets were characterized by X-ray diffraction (XRD)、scanning electron microscopy (SEM)、Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) et al. The effect of pH on the gas-sensing performance of CdGa2O4 nanosheets was investigated. The results showed that the sensitivity of CdGa2O4 which prepared by annealing at 700oC for 5h after precipitation at pH of 10 to 100 ppm formaldehyde was 316 at 110oC. The sensitivity of the gas sensor based on CdGa2O4 nanosheets to 0.01 ppb formaldehyde was 2.