Along with the operation of more passenger dedicated lines, the service environment of domestic high-speed trains becomes more complex, which brings new challenge to the safe and reliable operation of China high-speed trains. For researching the service performance of high-speed trains under the complex service environment, long service performance tracking of CRH3 series EMUs was carried in Wuhan-Guangzhou, Beijing-Guangzhou and Beijing-Shanghai passenger dedicated lines. A great lot of test data about service environment, service condition and service performance was obtained under operating condition of CRH3 series EMUs, and coupling analysis of test data was carried, by which, service performance variation rules of high-speed trains with service environment and service condition were obtained. This study made academic basis and guidance to the R&D and maintenance of high-speed trains.