Abstract: Affected by irregular plot，operation tracks of agricultural machinery are diverse，and difficulty of calculating operation area also increases.Effective and accurate calculation of agricultural machinery operation area is main basis for agricultural machinery operation supervision and efficiency evaluation.Through analysis of plots and trajectories，cubic spline interpolation algorithm was used to generate agricultural machinery operation trajectories，which could ensure smoothness of trajectories while passing through all trajectory points.The operation area could be calculated by accumulating all operation track lines and combining operation width.This method not only reduced error caused by unreasonable calculation of broken line method at corner，but also solved problem that small radian steering track line of other methods was not smooth in process of driving on arc plot.The accuracy of this method was higher than that of traditional broken line method.