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The paper develops an engine emission test driving cycle of heavy duty city transit buses. A real-world emission test is performed by PEMS in Guangzhou, Foshan and Shenzhen which are the three big cities in the Pearl River delta in southern China. Sets of 107767 data were sampled, including vehicle speed, transmission gears, and exhaust emission, etc. Engine speed and torque were calculated based on the vehicle speed and transmission ratio, then normalized and standardized. The methods of principle component analysis and cluster analysis were used for developing a driving cycle. The real-world continuous run mode was separated into1625 micro-trips, and 12 basic characteristic parameters were used to describe the characteristic of continuous run mode and micro-trip modes. Dimension of characteristic matrix of micro-trips was reduced by principle component analysis, and 1625 micro-trip modes were clustered into 5 categories.