Upgrade and application of the gas puff imaging system in EAST

•The EAST GPI diagnostic has been upgraded by developing a new relay optical system in 2020 and operated successfully since the spring campaign of 2021.•In contrast with the previous GPI optical system in EAST, the new relay optical system has much lower light loss; consequently, the image intensity and the GPI temporal resolution can be raised significantly, as demonstrated by the commissioning experiment of GPI in EAST.•The GPI diagnostic in EAST has a temporal resolution of 531645 Hz and a spatial resolution of 2 mm in the objective plan.•Clear edge fluctuations can be measured directly by the EAST GPI diagnositc, and the corresponding propagation velocities in the poloidal and radial directions are derived by the time-delay cross-correlation method.