The invention discloses a method for building a leaf in vitro regeneration system of begonia rex. The method comprises the following steps of: (1) selecting an explant and sterilizing the explant; (2) carrying out adventitious bud induced cultivation after cutting the processed leaves; (3) carrying out high-voltage electrostatic field treatment; (4) carrying out subculture proliferation cultivation on the adventitious bud induced by the leaves; (5) carrying out rooting culturing on a test-tube plantlet after the subculture proliferation cultivation; and (6) cutting and rooting. The begonia rex is subjected to tissue culturing by adopting the propagation method; the reproduction rate of a culturing period (51d) is 243.1 times; the propagation speed is fast; and the problem of seeding propagation of the begonia rex is effectively solved.