An electrode structure for an ion drift tube and an ion drift tube with the electrode structure are disclosed. The electrode structure comprises an annular electrode. The annular electrode has an inner edge bent towards one side such that a section of a central portion of the annular electrode has a swallowtail shape. With the ion drift detection instrument, ions in a drift state can travel along focusing electric lines of force, and since the high-voltage intervals between the electrodes are increased at a uniform acceleration, the generated electric field enables the ions to be in a uniformly accelerated drift state so that both the sensitivity and resolution of the mobility spectrum of the detection instrument can reach optimum.