Abstract: The load sharing non-uniformity coefficient of the planetary transmission is a core indicator for evaluating the uniformity of load distribution among planetary gears. Current research primarily focuses on theoretical analysis, with limited experimental testing, and suffers from issues such as insufficient measurement accuracy, inconvenient sensor placement, and low data processing efficiency. To address these challenges, a test method for the load sharing non-uniformity coefficient of planetary transmissions is proposed. By segmenting the sun gear into sectors, decoupled measurement of the coupled loads from multiple planetary gears is achieved, and the principles of measurement hole arrangement are defined. The tooth stiffness and strain consistency before and after segmentation are compared and analyzed to clarify the influence of the segmented structure on load sharing non-uniformity. Experiments are carried out on a six-planet-gear system, and the rotational speed versus non-uniformity coefficient characteristic curve is plotted. Experimental results show that the load sharing non-uniformity of this system is significant, and the non-uniformity coefficient exhibits a segmented variation pattern with rotational speed: first increasing, then decreasing, and finally stabilizing. This study provides methodological support for both theoretical analysis and engineering validation of load sharing non-uniformity characteristics in planetary transmissions.