Provided are a new precursor miRNA and the applications in tumor therapy thereof. The precursor miRNA, from 5′- to 3′-end thereof, has the structure represented by formula (I). B1 is an anti-miRNA and/or siRNA to be expressed; B2 is a sequence substantially or completely complementary to B1, and B2 is not complementary to C; C is a sequence with stem-loop structure; A1 and A2 are independently hydrogen or optionally a RNA sequence consisting of 4 to 5 bases. The precursor miRNA can be processed to form an anti-miRNA and/or siRNA in hosts.