Abstract: As many factors should be taken into consideration in well trajectory control of horizontal wells, in order to guarantee the successful target hitting, proper well trajectory parameters should be determined first. A kind of mathematic model was established during the process of kickoff section so as to draw a curve graph of the well trajectory to be drilled. In combination with the data and the curve graph, the implementation parameters could be determined. The actual application indicates the model is of being easily seen and simplicity and it proves to be a practical way to carry out well trajectory control.