The characteristics of laser induced damage morphology in the bulk of the K9 glass caused by focused nanosecond laser pulse is analyzed in detail. The damage shape looks like a spindle with a large front-end and its thickness gradually decreases on going to the rear end. According to the experimental results, the damaged range can be divided into four zones, namely the filamentary plasma channel, fractures, the fusion zone and the region of varying refractive index. The function of laser pulse energy deposition in space and the expansion pressure of shock wave are deduced, and the corresponding damage morphology is analyzed based on the spatial distribution of pressure. The theoretical analysis agrees with the experimental results.