Particle emissions from diesel engines are the primary contributor to the ultra-fine particle in the urban atmosphere, and have severely reverse effects on environmental quality and human health. In recent years, particle emission is strictly regulated in the emission legislations, which requires the higher performance of instruments for particle number measurement. In this article, five particle number measuring instruments are summarized in their measuring principles and features. Then, the performances of those instruments under specific requirements and operating conditions are compared. Finally, the accessibility of those instruments is analyzed for the measurement requirements of the upcoming emission regulations. The result shows that the condensation particle counter (CPC) has a faster response to detection of >10 nm particle number emissions, which can meet the test requirements of the urban RDE test cycle and 10 ~ 23 nm in future regulations. However, CPC cannot measure the particle size distribution, so it is not suitable for the development of controlling technology for 10~ 23 nm particles. The engine exhaust particle sizer (EEPS) can give a size distribution of as small as 5. 6 nm particles, which may provide complementary information for the CPC detection for the upcoming emission legislations.