Abstract: In this paper,based on the linearized two-layer barotropic primitive equation model,the spiral wave instability is studied in a circular vortex with basic flow of horizontal and vertical shear. It is shown that the unstable disturbance fields of thickness,divergence and vorticity have obvious spiral structure in the top and low layers of the vortex,when the basic flow is destabilized. The spiral structure of thickness fields is the most obvious. The spiral structure in the low layer is more complex than in the top layer. In the model,the greater the vertical shear of basic flow is,the easier the destabilization of basic flow is. The phase of unstable disturbance in the top layer is almost inverse to that in the low layer,so the structure of the spiral wave is corresponding to baroclinic model. The propagation of disturbance centers in the spiral wave in the tangential direction is opposite to the basic flow and the disturbance centers almost do not propagate in the radial direction. The whole movement of the spiral arms is slower. It is obvious that the magnitude of divergence field is greater than that of vorticity and the allocation of these fields agree with the inertia-gravitational wave,so the occurrence of the spiral wave can be due to the instability of the inertia-gravitational wave. The shape of the spiral wave in the model is similar to the spiral cloud (rain) band in real tropical hurricanes.