Thin-film diode structure is MgAl/PbPc/Cu if lead phthalocyanine is taken as organic semiconductor gas-sensing material with methods such as vacuum thermal evaporation or magnetron sputtering. Use Keithley 4200 semiconductor instrument and Gas-sensing measurement system to analyze gas-sensing characteristic of Schottky diode device, the sensitive degree of NO2 with different density can be compared through theoretical analysis of measured current and voltage data. The measurement result shows: when the device is placed in 10ppm NO2 environment, after 74 minutes, forward current is decreased by 65 times, the corresponding MgAl/PbPc Schottky barrier height rises about 20meV. Reversed current of the device is 4 times larger because the increase of minority carrier electron number in PbPc thin-film is being absorbed by NO2.