Accurate calculation of gas hydrate saturation is very important for resource evaluation. In this paper, the method of combining ultrasonic log data with the effective medium theory model has been effectively used to evaluate gas hydrate saturation characteristics of borehole formation in the Qilian Mountain permafrost. This method has been applied to the typical pore- filling gas hydrate borehole DKXX- 13. The compressional wave (P- wave) velocity simulated by the effective medium theory model is more consistent with the actual log data than the velocity model based on two- phase medium theory in the pore- filling reservoir. The range of the gas hydrate saturation of the typical pore- filling reservoir in hole DKXX- 13 is 13. 0%~85. 0%, with an average value of 61. 9%, which is in accordance with the results from the standard Archie equation and the actual core test. The research results could provide important reference for gas hydrate reservoir logging evaluation and seismic exploration in the Qilian Mountain permafrost.