In this work, we optimized a microbolometer for application of a $CO_2$ detector by using MEMS technology. We fabricated a stable thermal isolation structure by varying the lengths of supporting legs which affect bolometer performance. We could fabricate more stable thermal isolation structure for the microbolometer through the results of ANSYS simulations, and minimize the fabrication processes by using bulk micromachining to use a $CO_2$ detector. The microbolometer shows a detectivity of $2.5{ imes}109$ cmHz$^{1/2}$/W at a chopper frequency of 8 Hz and a bias current of $6.25;{mu}A$ with a vacuum package of about $3.0{ imes}10.3$ torr. Therefore, we put to conclusion that the microbolometer optimized in this experiment could be useful for the application of a $CO_2$ detector.