Abstract: This paper presents a new method of estimating the amount of forest trees using aerial photography data. It is an important property that can quantitatively process the images of remote sensing directly,and recognize and extract the hidden signals of ths images.Its basic principle is that the system model which is set up to meet the requirement of utility must preserve equality between the input-output change of modelling and that of true system. Some testing experiments have been done in the forest regions in the northeast of China using this method.(1)Digital processing technique was used on the airphoto data of No.25 sample ground at Daxinggou in Jilin Province.(2)ISODAT 1 utility program was made on the basic of the ball model.(3) Iterative calculation was run by TRS-80 I microcomputer.The experiment result has proved itself to approach to the true data,and its error is not more than 10 percent. The paper analyzes the basic theory of the method and presents the course of the experiment,the utility program and the initial result.