The invention relates to an on-site quick detecting device for content of acetylene gas dissolved in oil and a detecting method thereof. The on-site quick detecting device comprises a closed type oil-testing degassing device, wherein a gas chamber and an oil chamber which are up-and-down connected with each other are arranged in the inner chamber of the oil-testing degassing device; an oil inlet and an oil outlet are respectively formed at the top and bottom of the oil-testing degassing device; the oil inlet is penetrated through an oil gas separating filter screen and extends into the oil chamber; an oil draining valve is arranged on the oil outlet; a stirring paddle is arranged at the center of the bottom of the inner chamber of the oil-testing degassing device; four ceramic heaters andtemperature-sensing probes are arranged in the inner chamber of the oil-testing degassing device; the on-site quick detecting device further comprises a pressurizing air pump; an air outlet of the pressurizing air pump is connected with the gas chamber through a gas feeding pipe; the gas chamber is connected with a detecting pipe through an air exhausting pipe; the pressurizing air pump, the oil draining valve, the motor, the ceramic heaters and the temperature-sensing probes are all electrically connected with a controller. The on-site quick detecting device has the beneficial effects that the acetylene gas dissolved in oil can be quickly detected on site, the fault nature can be quickly judged, the detection process is automatically controlled and the operation is simple.