The thermomechanical noise and frequency response of uncooled bi-material microcantilever IR detectors based on MEMS technology depends on the dimensions and space environments. In this paper, Analysis of frequency response and noise in the SiO2/Al microcantilever IR detector are presented by changing the thickness of the layers and the width of the bi-material and isolated legs in the vacuum and air space environments. The results of the numerical analysis show that the detector responses are increased by decreasing the thickness of the insulation layer and the width of the legs. If the thickness of the insulation layer and the width of the legs are 10 μm and 1 μm, respectively, and the thickness of the SiO2 layer is twice the thickness of the Al layer, the thermal conductivity and time constant are reduced 128.5 and 123 times, respectively, and the temperature, displacement, power sensitivity increased 125, 124.7, and 127.6 times, respectively, in the vacuum environment compared with the air environment. The results of the frequency analyze show that thermal video frame rate and thermal imaging accuracy increase in the air environment, but thermal imaging accuracy is increases in the vacuum environment, since the time constant increases due to decrease the thermal conductivity in the vacuum environment. The noise analyze results also shows that noise is improved and temperature fluctuation noise, background fluctuation noise, thermomechanical fluctuation noise and total noise equivalent temperature difference in vacuum reduce to 1.38 mK, 1.24 mK, 2.3 mK, and 1.86 mK, respectively.