The invention provides a method and device of determining low frequency wave impedance, wherein the method comprises: obtaining a logging low frequency wave impedance model and an earthquake data low frequency wave impedance model; comparing and analyzing two models according to frequency ranges to obtain a compensation coefficient and perform compensation; and fusing models of different frequency ranges to obtain a fused low frequency wave impedance model. According to the embodiment of the invention, a finally obtained low frequency wave impedance model with logging and earthquake information fully combines well boring, geology and earthquake information, and accordingly has a higher transverse resolution. The method solves the technical problem of inaccuracy of a low frequency wave impedance model built by the prior art, effectively improves the accuracy of the low frequency wave impedance model, and further improves the lithology prediction accuracy of the wave impedance inversion technology.