Abstract: A novel Micro-Machined Pneumatic I nfrared Sensor is described,which is classified as a uncooled infrared sensor.The sensor consists of asmall cavity filled wi th aspecial gas,which shows a characteristic spectral sensitiv ity in the wavelength range of the inf rared light.Infrared intensity is measured via the deflection of the me mbrane induced by thermal expansion of the special gas.In order to study and optimize this sensor,a thermal model of the sensor structure is developed,and the commercial finite-element analysis program ANSYS/FLORTRAN^® is employed for fluid-structural coupling.The temperature distribution of membrane,pressure distribu tion at fluid-solid interface and deflection of diagram are obtained.