Method of controlling gas heat-pump system

Proposed is a method of controlling a gas heat-pump system, the system including an air conditioning module having a compressor and indoor and outdoor heat exchangers, and an engine module having an engine combusting mixed gas and thus generating drive power for operating the compressor, the method including: measuring factors that are temperature and humidity of outside air, an rpm of the engine, intake pressure, and an air-fuel ratio, the factors having effects on driving of the engine in an operating environment where the engine is driven; measuring a necessary ignition voltage for an ignition coil in a manner that corresponds to at least one of a plurality of the measured factors; and calculating a dwell time at which the necessary ignition voltage is output by the ignition coil.