The embodiment of the invention provides a method and device for determining an oil and gas reservoir, and the method comprises the steps: obtaining the converted shear wave seismic data of a target region; determining a shear wave speed frequency dispersion attribute parameter according to the converted shear wave seismic data; and determining the oil and gas reservoir in the target region according to the shear wave speed frequency dispersion attribute parameter. Because the scheme gives consideration to the specific characteristics of the shear wave speed frequency dispersion attribute parameter, the shear wave speed frequency dispersion attribute parameter is determined according to the converted shear wave seismic data, and the oil and gas reservoir in the target region is recognizedthrough the shear wave speed frequency dispersion attribute parameter, thereby preventing a conventional converted shear wave seismic exploration method from damaging converted shear wave seismic amplitude, solving a technical problem that the determining of the oil and gas reservoir through the conventional method is bigger in error, and achieving a technical effect of accurately and efficientlyrecognizing the oil and gas reservoir in the target region.