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. Finally, an engine driving cycle W1900 of city transit buses was constructed with the representative micro-trip modes. It's found that the conformity degrees of characteristic parameters of W1900 with that of total samples are more than 89% which shows W1900 has a good conformity with total samples.Compared to ETC, W1900's average speed is 33% lower, average torque is 16% lower and average positive torque is 23% lower, but percentage of idle mode is 5.64 times of that of ETC. It means W1900 can better reflect the driving condition of transit buses in the Pearl River Delta in southern China than ETC.