The Harmony high-power electric locomotive, weighing 150 tons and with a pulling force of 5,000 tons, is the most widely used locomotive in Chinese railways currently. Just like cars, which needs maintenance after a certain mileage, locomotives need overhaul after having run over 1 million kilometers. Xi'an locomotive repair depot is an overhaul base for Harmony locomotives, in other words, the "4S store" of locomotives.

Xi'an locomotive repair depot undertakes the mission of overhauling the 1,400 locomotives serving in northwest China. 

In this base, disassembling, cleaning, testing, assembling, through all these procedures, the tired or ailing locomotives have regained strength and energy and are ready to go back to the rail again.