Factors for maintaining the balance in the upperlevel momentum over East Asia have been calculated using observational data for January and July. The lowest order approximation is found between the dynamic generation term and the horizontal transport divergence. The dynamic generation (dissipation) with net output (input) corresponds to the entrance (exit) of the jet stream in the middle-upper troposphere. During January a couple of areas for dynamic generation with output and dissipation with input of zonal momentum are observed over China’s mainland and the central North Pacific and daring July over Northwest China. The vertical transport and the effect of subgrid-scale processes must be taken into account in the first order approximation balance and, in addition, the effect of transient motions must be included in the maintenance of monthly mean circulation.