Abstract: In this paper,the regional protective effects of farmland windbreak network were calculatedwith a geoctrophic deviation method,the reliability was analysed and the value of the method was applied.The value of protective effects of farmland windbreak network at H(the height of tree) was alsocalculated in the northern coastwise of Jiangsu Province.It is found that(1)protective efficiency ofwindbreak network is 15 %～45% and if the wind force is different, the proteCtive ability is distinct:the stronger the wind is,the more the extent of that is weakened;(2)the influence to the wind direction by the windbreak network is not large;(3)not only the perturbation motion strengthens inside thewindbreak network,but also such a region exists to a certain range outside.