Uncertainty components and evaluation of the system of pressure measurement are presented in this paper. Since early in 1980s, measurement uncertainty is getting more important due to ISO/IEC 17025, which is established for international test and calibration laboratories. Up to now it is true that accuracy, precision, error and etc. have been commonly used in industry to define the amount of error to the products and equipment, but these terms ought to be united into uncertainity in the future. This paper describes how to indicate measurement uncertainty and types of measurement errors, and then shows the evaluation result of measurement system using piezoelectric pressure transducers.