Provided are a precursor miRNA and application thereof in a tumor treatment. The precursor miRNA from the 5' end to 3' end has a structure presented as formula I:B1 is anti-miRNA-214-5p； B2 is an essentially complementary sequence or a totally complementary sequence to B1, and B2 and C are not complementary； C is a sequence having a stem-loop structure； A1 and A2 are respectively RNA sequences having no or 4-5 bases freely selected bases respectively； the precursor miRNA shown can be processed to form anti-miRNA-214 in a host, and only anti-miRNA-214-5p but not anti-miRNA-214-3p is expressed in the anti-miRNA-214.
