In flight test,in ordor to reflect actual status of technical parameters, flight test system must provide accurate data, including many processes, flight test system’parameters must exist error. To meet the precision requirements,this text analyzed the possible processes that bring error, illustrated by the example of pressure parameter, starting with the method of "six Sigma" definition, measurement, analysis, improvement and control of the five processes, with three airplane’s pressure sensor calibration original data as samples, analyzed precision results, and educed that in advance to confirm specific pressure change interval parameters, according to the distribution characteristics of the test system precision to choose appropriate sensors to meet precision requirements, analysis of pressure parameter error in flight test by 6 Sigma methods is possible. Finally educed conclusion that generalized to other test parameters error analysis can lead us match the instruments rationally and meet the precision requirements.