The invention discloses a method and device for testing atmospheric ion mobility.The method includes the steps that the distance d between an upper pole plate and a lower pole plate and ambient air pressure, temperature and relative humidity are determined; an equation set of the electrode field Ed of the lower pole plate and the voltage VT of the upper pole plate is determined, the equation set of Ed and VT is jointly solved to obtain ion mobility k, and the voltage of Vco and VA is adjusted so that a corona inception thin wire network can conduct corona discharge; VT is adjusted so that corona charges can reach the lower pole plate through the upper pole plate; the electric field intensity Ed and the ion current density J at the lower pole plate are measured; VT, Ed and J are substituted to an equation of the ion mobility k, and the ion mobility is obtained.According to the method and device for testing the atmospheric ion mobility, the ion mobility is obtained directly through strict equation solving, it is unnecessary to suppose that E0=0, and thus the result is more accurate; the ion mobility can be obtained just through a group of testing data, and it is unnecessary to measure a large number of points to find a curve with IT changing but the ion current density J of a testing region tending to be saturated.