Abstract: This paper introduces a newly developed portable on-site vacuum gauge calibration apparatus and analyzes its measurement uncertainty. A portable on-site calibration apparatus was developed, in which the dynamic comparison method and the dynamic flow method are coupled to achieve a calibration range of (10⁻² to 10⁻⁵) Pa, meeting the urgent need for field calibration of vacuum gauges in scientific research and industrial production. The calibration results involve multiple parameters, including chamber pressure, inlet pressure, molecular conductance values of both inlet and pumping flow elements, and backstreaming ratio, and since ambient temperature variations during field calibration will affect these parameter values and their corresponding uncertainty components, proper analysis and evaluation of measurement uncertainty are crucial for ensuring the accuracy of field vacuum gauge measurements. Based on the device's measurement principles and uncertainty evaluation theory, this study establishes the corresponding measurement model and analyzes each uncertainty component and its temperature dependence using actual experimental data. The evaluation results show that when calibrating in field environments with temperatures of (25±15)℃ and maximum fluctuations of 5℃ (±2.5℃), the device achieves measurement uncertainties of 2.4%~3.2% (k=2) using the dynamic comparison method and 6%~7% (k=2) using the dynamic flow method.