In this paper, we study the self-trapping of a Bose-Fermi mixture in a periodic modulation field by adjusting fermionic number and interaction parameter in a double-well potential. We find that the self-trapping of bosons can be affected by interatomic self-interaction and interspecific interaction parameter. Moreover, we notice that the self-trapping of bosons gives rise to a critical phenomenon with the variation of interaction strength and fermionic number.