The linearized C-W equation is used very expediently, but it has the problem of inaccuracy. An improved equation based on C-W equation was presented, which can describe the formation flying more accurate. Firstly, the derivative process of C-W equation was analyzed and the inaccurate reason was find out. Then parts of contents were adding and re-derivation, which has been ignored in order to simplify the equation in the original derivative process. And lots of mathematical transformations were used to reduce the new equation. Finally, a set of linear differential equations with constant coefficients was given, which can improving the precision without increasing the complexity. Simulation shows that in the condition of circular orbit, the accuracy was improved a lot comparing with the C-W equation, while in nearly circular orbit, the long-term error of C-W equation was eliminated.