Abstract: To improve the ability of detectivity for infrared detectors with different wavebands,a cascode CTIA ROIC composed of mosfets and capacitors is optimized.Firstly the ROIC which consists of cascode integrator,sourse follower and sample hold circuit is given.The noise model is built stage by stage,the effect on the noise due to the mosfet integration capacitor bandwith limited capacitor and SH capacitor is analyzed.Three significant conclusion has arrived:(1) proper gm design could effectivly suppress the noise of mosfet,which resulting to the lowest value,approximately 2/3KTC noise of bandwith capacitor;(2) the closer the values between intergrator capacitor and SH capacitor,the lower noise the ROIC has;(3) the difference of radiation characterisic between the midwave infrared and shortwave infrared leads to the giant diversity of the designing value of intergator capacitor,focusing on the typical application,the best value of integrator capcitors are 1.7pF and 0.76 pF for midwave and shortwave respectively.