Abstract: The grade of land in the city zone is affected by nature and society position plus communication condition.The process of land grading is to get the fixed quantity of all conditions and to classify all the land parcel to be evaluated。It is important to get the effect value from that the evaluated land parcel is affected by the grade factors in the process of land grading.Same type factors' effect attenuates with the increase of distance between grade factors and evaluated land parcel.The attenuating rule is called distance-attenuating formula.Traditionally,the distance between grade factors and evaluated land parcel is the length of spatial line from the center of factors to the center of the land parcel when the effect value of grade factors is calculated.It ignores the obstructions between grade factors and evaluated land parcel.So the graphs that effect value is represented are a series of contour lines with attenuating effect value.In people's custom thought,the distance from here to there is the distance along the road instead of the spatial distance.So it is more reasonable to use the distance along the road than to use the spatial distance in land grading.In this paper,the shortest path method in graph theory used in urban land grading is discussed.The distance between grade factors and evaluated land parcel is calculated by the shortest method.The effect value of grade factors in each unit is gotten by the distance-attenuating formula.Based on the value,the more reasonable land grade of each unit can be reached.