The invention discloses a sulfur hexafluoride insulation electrical equipment decomposition product detecting device and method. The sulfur hexafluoride insulation electrical equipment decomposition product detecting device comprises a gas circuit module, a light path module and a control module; the gas circuit module comprises a first solenoid valve, a first flow control valve, a second flow control valve and a second solenoid valve; the light path module comprises a laser, a light splitter, a standard gas chamber, a second photoelectric detector, an optoelectronic isolator, a collimator, a first reflection mirror face, a ring-down cavity, a second reflection mirror face and a first photoelectric detector; the control module comprises a signal modulation module, a laser driving module, a temperature control module, a signal collecting module and a master controller. By means of the sulfur hexafluoride insulation electrical equipment decomposition product detecting device and method, accurate detection on sulfur hexafluoride insulation electrical equipment decomposition product hydrogen sulfide gas can be achieved, the device is in modular design, the structure is simple, and the reliability of the detecting device is improved.