Northern Hemisphere 500 hPa monthly mean geopotential height fields have been used with the tropical part interpolated reasonably,and coefficients of spheric functions therefrom of the hemispheric height fields have been found for January and July over a range of years. On this basis,the spectral structures of these functions for long-term mean 500 hPa height in the two months have been investigated,showing that the structures are marked by low dimension and order,and the major circulation features and seasonal variation of the height can be portrayed in terms of 20 or so spherical function components.