The op timization design on the main parameters of high-resolution thermo-imaging system with great Fvalue is discussed. These parameters include the F /# value of the detector,waveband, valid electronic bandwidth and opti-mal dimension of the detector. We have provided primary test resultwhen F /# is 4, and forecast the NEDT, resolution level of focal plane that thermo-imaging system with different F /# value can arrive. Conclusion: adop ting the large F /# optical system and detector is effective method of designing the high-resolution thermo-imaging system.