In order to enrich the theory of space electro-optical technique, break through technical bottleneck of laser communication ranging integration in medium region, this paper proposes a laser triangulation ranging model with dynamic scale. Firstly, by analyzing main technical constraints of different high-precision laser ranging in medium region, defeats and shortages in terms of measurement accuracy of traditional triangulation method are showed and demonstrated. On this basis, based on the electric vacuum semiconductor composite detector model system, it is proposed that a dynamic scale mechanism can effectively extend the measurement range of the laser triangulation ranging in medium region, then make up for the vacancy of the above integration system in medium region. The correctness and effectiveness of the model are verified by theoretical analysis, parameter calculation, system design, simulation and experiments, the measurement resolution of the triangulation ranging model with dynamic scale proposed by this paper can reach one thousandth of measuring range, which can fully satisfy the needs of subsequent engineering and systematic design.