The invention provides a calculating method and device of a stratum quality factor. The method comprises the following steps of according to seismic data, calculating a first amplitude spectrum corresponding to a first moment and a second amplitude spectrum corresponding to a second moment; carrying out low pass filtering processing on the first amplitude spectrum and the second amplitude spectrum, and acquiring the first estimation value and the second estimation value of corresponding seismic wavelet amplitude spectrums respectively; and according to the first estimation value and the secondestimation value, using a spectral ratio method to calculate the stratum quality factor. In each embodiment of the invention, tedious parameter settings and complex calculating processes during the process of estimating the quality factor by using the spectral ratio method in the prior art are reduced; the accuracy of a stratum quality factor calculating result is increased; the automation of stratum quality factor calculating is realized; manpower is saved; the interference of a human factor to an estimation result is reduced; and the method and the device are high-efficient and practical.