To test and reflect the influences of objects, instruments, methods, and conditions on results and to obtain more reliable and accurate representative values of the mechanical parameters of pavement materials, this study was based on the theory of measurement uncertainty. It used cement stabilised aggregates and AC-16C asphalt mixtures as study objects and proposed using synthetic standard uncertainty instead of standard deviation in calculating the representative value to determine the standard deviation of measurement results. The synthetic formula was employed to determine the standard variance of measurement results. The results were evaluated with class A and class B uncertainties and verified by the Monte Carlo method (MCM). The results indicate that using synthetic standard uncertainty instead of standard deviation to calculate the representative value for structural design is more conservative and accurately reflects the actual project situation. The representative value of pavement mechanical parameters obtained based on measurement uncertainty theory effectively reflects the uncertainty of the mechanical parameters of the pavement material. This, in turn, affects the uncertainty of the pavement structural mechanical calculation and the pavement performance in the later stages of the project. The “Guide to the Expression of Uncertainty in Measuremen” (GUM) is applicable to the measurement uncertainty of pavements. While the GUM has a wide range of applicability, it presents significant errors for nonlinear measurement models and mathematical models with strong correlation components. Compared with the MCM, the evaluation process of GUM is relatively complex and prone to errors. The findings of this study are expected to provide a reference for accurately evaluating the representative values of typical mechanical parameters of pavement materials, thereby promoting the widespread application of measurement uncertainty evaluation theory in design, construction, and quality control.