Abstract: The influence of eddy viscosity on the distribution of quasi-stationary planetary waves in the subtropics in summer is analysed theoretically. It is found that since the basic flow is very weak, the eddy viscosity may play an important role for planetary-scale motion in the subtropics in summer.A linear, quasi-geostrophic, 34-level spherical coordinate model is also utilized to calculate the difference of quasi-stationary planetary waves and quasi-stationary disturbance pattern in response to forcing by topography and heat sources under the different eddy viscosity. The computed results show that the eddy viscosity coeffiecient largely influence on the strength of planetary-scale circulation in the subtropics in summer.