Study is undertaken of basic characteristics of summer quasi-stationary circulationsystems(QSCS)and their intramonthly evolutions by use of a zonal coupled(seaair and land-air)model.Results show that at Northern Hemisphere extratropics,the high-and low-levelQSCS’s are all featured by a zonal bi-wave structure,in complete agreement with the landseadistribution over the belt,thereby confirming that the geographic pattern is the underlying causeof the QSCS’s which show temporal variation largely in the first 20 model days,with the area ofstrongest change generrally being the core of the system.