The flow condition of non aantropic relhgerant mixture HFC 32/HFC-134a flowing through the capillary tube has been analyst. Based on the fundamental equations of the fluid flowing through the capillary tube and considering jointly the fixture's characteristics, the throttle procedure of non-aantropic refrigerant mixture has been described using mixing principle. The mathematial model has been established and the optimum length of capillary tube with various pressure difference has been calculated.