With the decreasing of the key size of InSb infrared detector, the influence of the passivation film stress on the I-V performance of the device becomes more and more obvious. In order to reduce the stress of the detector chip, a composite passivation film system consisting of SiO₂ and SiON was studied. Passivation films with thicknesses of 300 nm, 500 nm, 700 nm and 900 nm were deposited on InSb wafers by varying the radio frequency (RF) time of the gas. The stresses of passivation films with different thicknesses were measured and calculated. When the thickness is 700 nm, the minimum stress of the passivation film is －1.78 MPa. The I-V characteristics of devices with different stress passivation films are investigated. It is found that the InSb chip has better I-V characteristics when the thickness is 700 nm. By adjusting the thickness of composite passivation film, the stress of passivation film is reduced, and the performance of InSb detector is effectively improved.