Thin films have attracted much interest because they often have novel properties different from those of their bulk counterparts. In this work, we tune two metastable states in three kinds of lanthanum cobalt oxide thin films by electron beam irradiation and record their dynamic transition process in situ in a transmission electron microscope. The lanthanum cobalt oxide thin films exhibit a homogeneous microstructure in the initial state and then transfer to a stripelike superstructure with 3a(0) periodicity (a(0) is the perovskite lattice parameter), further developing into a superstructure with 2a(0) periodicity in dark stripes (brownmillerite structure). To explore the inherent energy discrepancy within the two metastable states, we perform first-principles calculations on a LaCoO3-delta (0 <= delta <= 0.5) thin film system by geometry optimization. The calculation results suggest that the forming energy of the 3a(0) periodicity stripelike structure is a little lower than that of the 2a(0) periodicity in the LaCoO3-delta thin film. Our work explains why the two stripelike structures coexist in lanthanum cobalt oxide thin films and extends prospective applications related to oxygen vacancies in thin films.