Abstract: Basing on the single and miltiple bick scattering model of seismic coda wave, simplified attenaation equation in which the amplitude A of the seismic coda wave decreases with time t has inferred. A(f/t)=c.C.e^πft/Q Using the seismic record dita of partial seismic stations in Tianjin area, we have computed the Q value for different medium and obtained the A-T attennation curve for the different Q-value at f=1. Because of thicker loose sedimentary layer in Tianjin area, lower Q-value has been obtained by ground record data. But higher Q-valie has been obtained by borehole record data, which approaches to that in base rock aieas with the depth of the borehole.