The mass of uranium in a fuel element is a critical parameter for high-temperature reactor (HTR), in that accurately measuring and controlling the mass is essential for reactor physics and nuclear material accounting. Currently, the measurement of uranium mass in sphere fuel elements primarily relies on the weighing method during,fabrication supplemented by destructive sampling inspection. There is a lack of accurate non-destructive uranium loading detection methods for new sphere fuel elements to support inspection for a certain scale. This research discusses the feasibility of establishing a non-destructive uranium mass detection device from the perspective of measurement error analysis. It constructed an ideal fully enclosed detection model and simulated the process of detecting γ emitted during the natural decay of new sphere fuel elements by the Monte Carlo (MC) code package of Geant4. This research analyzed the effects from the variability in the dimensions and physical properties of TRISO particle kernels, coated layers, the non-uniformity of TRISO particle distribution, variations in the dimensions of the fuel and non-fuel regions, and changes in the physical properties of the matrix material and so on. The result disclosed the limitation of non-destructive uranium mass measurement in the view of precision based on characteristic radiation emitted by the fuel, which can provide a reference model for the design of practical devices.