This paper described that the growth of cotton yield per mu in Hubei province is greater in the north than in the south.Analysing the relations between the cotton yield and rainfall, the author discovers that the quality of rainfall and the degree of drought or waterlogging are the main factors affecting cotton yields.The years in which the average yield per mu dropped 15% were those when the rainfall between June and August was abnormal while the years in which the average yield increased more than 20% were years when the rainfall in these three months were normal.In years of excessive rain, the rainfall between June and August was more in the south than in the north, and in years of drought, in reveres, so the calamities of drought or waterlogging were more severe in the south than in the north.However in years of good harvest, the rainfall was adequate and had not much difference between the north and the south.By calculating the variability of rainfall between June and August, the author finds that the variability of rainfall is also greater in the south than in the north This shows that the rainfall is less changing in the north than in the south, and coincides with the fact that happens drought or waterlogging in the successive years.Approaching the ratio of input and output which is a good economic index, the author demonstrates that the economic benefit in the north is greater than in the south.Based on the above analysis and in consideration of the rational distribution of cotton fields the paper expounded a strategic assumption of shifting northward the cotton fields in Hubei province.