Abstract: With implementation of standard HJ 1014—2020 "Technical Requirements for Pollutant Emission Control of Non-Road Diesel-Powered Mobile Machinery", stricter requirements for emission control of non-road diesel-powered mobile machinery have been put forward．A certain corn combine harvester model was selected as test subject, and a portable emissions measurement system（PEMS）was used for testing．Emission test data were calculated and processed by using work-based window method, and factors affecting validity of test results were systematically investigated．According to PEMS testing process, critical considerations that should be noted during testing were systematically summarized to provide reference and suggestions for efficient and reliable implementation of PEMS testing for corn combine harvesters．