Abstract: For the location problems of traffic observation points for estimating Origin-Destination(O-D) matrix by flows on road section,the improved location rules for traffic observation points are proposed according to the concept of maximum possible relative error,i.e.,the rules of path covering and minimal traffic observation points,and a corresponding integer programming model is established.The model with simple structure can be readily calculated and needs less initial conditions,and it can not only guarantee the feasibility and precision of OD matrix estimation,but also economize the costs of traffic observation.The rationality and reliability of the result are illustrated with a road network example,and the applicability of the model is proved.