In this paper, we present a new method to determine the first ionization limit of europium atom. Firstly, time delayed field ionization is used to detect highly excited Rydberg states of europium atom. Secondly, reversed static electric field is used to exclude ion signal from photoionization, autoionization and other path. The law of first ionization limit shift of europium atom in electric field is studied. First ionization limit in zero electric field is deduced from data of first ionization limit shift in electric field. This value is well coincident with the reported values deduced by other methods.