The Berry phase of an effective Hamiltonian at low energy case of monolayer phosphorene was calculated,and compared with the Berry phase of graphene. It was found that external magnetic field could influence the Berry phase of the monolayer phosphorene. The Berry phase of the monolayer phosphorene could be adjusted to integral multiple of π by external magnetic field. Therefore,it was possible to realize quantum Hall effect in monolayer phosphorene by external magnetic field.