Targeting the critical need for efficiency and thermal management in helicopter transmission systems, this study focuses on the power loss of high-speed rolling bearings under oil-jet lubrication — a dominant lubrication method in such systems. To address this issue, this paper establishes a localized mathematical model for predicting the power loss of rolling bearings under oil-jet lubrication. The model’s completeness is enhanced by incorporating two key mechanisms: the dynamic load effect on rolling elements at high speeds and the oil shear drag loss at the bearing inlet interface. Based on this model, the power losses of several typical bearing types under identical operating conditions with low radial load are calculated. To validate the model, a dedicated test rig was built to conduct oil-jet lubrication experiments under the same low-load condition. Although this specific loading condition imposes certain limitations on the model’s applicability, the experimental results can still be used for model verification. The results show that the theoretical predictions agree well with the experimental data in overall trend. Further analysis reveals the variation patterns of individual loss sources with rotational speed, particularly the contribution proportion of the newly introduced power loss terms, thereby validating the correctness and necessity of the supplemented mechanisms. This study provides a generalized model and a theoretical basis for optimal bearing selection and loss suppression, directly supporting efficiency improvements in helicopter transmissions.