SnO2-In2O3 composite nanofibers of formaldehyde sensor were prepared by the double jets electrospinning method. A new film. type formaldehyde sensor was designed with SnO2-In2O3 composite nanofibers transferred onto an alumina ceramic tube with Au electrodes. The crystalline phase and microstructure of SnO2-In2O3 composite nanofibers were displayed using X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM), formaldehyde adsorption intensity and electrochemical mechanism of SnO2-In2O3 composite nanofibers were analyzed by oxygen temperature programmed desorption (O2-TPD) and X. ray photoelectron spectroscopy (XPS). These characteristic tests of formaldehyde sensor were carried out on the traits of sensitive performance, temperature, relative humidity, dynamic response, interference and stability by the XEDWS-60A type multifunction analyzer in gas sensor static test system. the results demonstrated that formaldehyde sensor based on S50 composite nanofibers with 240 nm sensitive film thickness, when the operating temperature was 500 degrees C and formaldehyde concentration was increased from 0.5 to 50 mg/L, the best linearity and sensitivity of formaldehyde sensor were 96.8% and 97.5% respectively, and its high temperature level was 1000 degrees C, the dynamic response time and recover time of formaldehyde sensor were 23 and 12 s, respectively. This kind of sensor showed good anti. disturbance to these gases, such as CO, NOx, toluene, phenanthrene, acetone, and methanol. The response value of formaldehyde sensor was attenuated about 5.5%, when formaldehyde sensor was applied continually on the automobile about 12 months, and its normal time was 6.4 months.