The problems of high manual labor intensity as well as high harvesting cost become more serious for Camellia oleifera industry, which promote the research of Camellia oleifera harvesting technologies with high efficiency. In order to effectively improve the energy utilization rate of mechanized harvester of Camellia oleifera fruit, the cable-driven excitation approach was employed with negligible cable mass to replace the traditional rigid vibration. Based on a bifurcated basic unit of tree, cable-tree reduced system was constructed with considering two constrained cables. The energy transfer mechanism in the reduced system was investigated to deduce the calculation formula of natural frequency. An ideal truncated cone model with variable circular cross sections for branches was utilized, and the measurement approach of measuring elasticity modulus of branches with variable cross-sections was presented. Taking Camellia oleifera varieties in Hunan Province as an application example, the basic parameters of the tree and the cable were measured, the natural frequency of the cable-tree reduced system was obtained. The theoretical values of the natural frequency for the cable-tree reduced system were compared with simulation and the experimental results. It showed that the relative errors of simulation results and theoretical results were less than 6.4%, the relative errors of the experimental results and the theoretical results were less than 8.6%, which verified the efficiency of the proposed calculation formula of natural frequency for Camellia oleifera with constrained cables. By comparing the resulting modulus of elasticity from the presented measurement approach and the conventional three-point bending test, the relative measuring error was within 7% and thus the feasibility of the presented measurement approach was validated. The research results can provide a theoretical basis for the design of a flexible cable-driven branch-vibrating harvester for Camellia oleifera fruits.