In order to develop infrared imaging technique based on parametric up-conversion, according to the up-converter model which can transform 10.6 μm radiation into visible light range, the phase matching angle, walk-off angle, acceptable angle and efficient nonlinear coefficient of GaSe, ZnGeP2 and AgGaS2 crystals with different phase matching methods were calculated. The results were well analyzed and compared. It is found that ZnGeP2 and AgGaS2 crystal are ideal up-converters because both of them can employ noncritical phase matching method and their acceptable angles are bigger than six degree, and nonlinear coefficient of ZnGeP2 can achieve 75 pm/V. The numerical simulation result gives a well theoretical instruction to up-conversion experiment of long wavelength infrared radiation(LWIR).