Exhaust emission from the diesel engine in transportation is one of the essential sources that cause air pollution, of which the primary pollutants include particulate matter, nitrogen oxide, hydrocarbon, carbon and oxygen compounds, which have significant differences in emission characteristics under different working conditions. We collected, organized and summarized the research on diesel exhaust pollutants emission and emission reduction measures in the past five years, and discussed the emission characteristics of diesel exhaust pollutants under different working conditions(altitude, speed, engine speed and load). The results showed that the pollutant emission was the most serious under the high speed of engine conditions in high altitude areas. Moreover, the analysis of the influencing mechanism found that different working conditions mainly affect the combustion temperature, oxygen intake, oil and gas mixture, combustion time and other factors, and then affect the formation of different pollutants. Furthermore, we summarized the measures and influencing mechanisms to improve the pollutant emission from exhaust emission of the diesel engine. This paper will provide theoretical guidance for the study of pollutant emission characteristics of a diesel engine under different working conditions. So far, there are many studies on typical pollutants in diesel engine exhaust, but few studies on the emission characteristics and generation mechanism of toxic and harmful substance such as persistent free radicals in particulate matters and gas-phase substances. However, the environmental risk of persistent free radicals may be higher than that of typical pollutants, which will be a major content in the study of diesel engine exhaust pollutants in the futures.