Uncertainty analysis is a method of expressing precision of test result quantitatively.A complete thermal efficiency experiment must include the uncertainty analysis to the result.The calculation method of uncertainty in ASME PTC 4-2008 was presented.On the basis of the thermal efficiency test for a 1 000 MW unit coal-fired boiler

the uncertainty of the measured thermal efficiency and corrected thermal efficiency was evaluated.The results revealed that the main factors affecting the uncertainty of the results consisted of the carbon content

exhaust temperature

and so on.Therefore

to reduce the uncertainty of the test results

that of the above parameters should be decreased.