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The measurement of tree diameter at breast height (DBH) is an important parameter for evaluating site quality and tree growth status. An ordinary digital camera was used to randomly shoot plot that was measured in an up and down direction. And the length of object should be measured so as to reversely deduct the position of photographic baseline and recovery the true spatial scale of photography area, achieving the aim for measuring the DBH of sample trees in the plot and the coordinate of the trees center. This research was based on theory of photogrammetry and carried out with the coplane of rays from same point and photographic as the conditions. Aiming at the limitation of photogrammetry, this research established the photogrammetry mode mainly in a vertical ground direction. The validity of the proposed algorithm was analyzed and verified in the experiment. Software of ground stereo photogrammetry system was developed, taking Microsoft Visual Studio as development platform. Twentyfive standing trees in five plots were measured and calculated. Experiment results demonstrated that the precision of DBH measurement using ordinary digital camera was high, and the experimental data were in good agreement with the actual, with the average absolute error of 0.29cm, and the average relative error of 1.99%, which were in line with the tree diameter at breast height measurement accuracy of national forest resource continuous investigation. With the constant increase of field working cost, people will pay more attention on the utilization of portable instruments in measurement. Therefore, the method has practical application prospect in forest resource survey.