The BiFe0.95Zn0.05O3 (BFZO) thin film was fabricated on indium tin oxide/glass substrate using a metal organic decomposition method combined with sequential layer annealing. Double ferroelectric hysteresis loops were observed in the as-deposited film, indicating that the film is partially aged. This aging phenomenon can be attributed to the formation of defect complexes between oxygen vacancies and acceptors of (Zn-Fe3+(2+)) in the film. The nonreversible transition from double ferroelectric hysteresis loop to the single one can occur during the course of increasing the applied electric field. More importantly, an asymmetry of the coercive field can be found to be strongly dependent on the magnitude and frequency of the electric field. This phenomenon was discussed based on the asymmetric driving force for domain backswitching in BFZO film with a preferential polarization.