Strongly correlated electronic system contains strong coupling among multi-order parameters and is easy to be efficiently tuned by external fields. Cobaltites (LaCoO₃) is a typical multiferroic (ferroelastic and ferromagnetic) materials, which had been extensively investigated over decades. Conventional research on cobaltites has focused on the ferroelastic phase transition and structure modulation under stress. Recently, researchers have discovered that cobaltite thin films undergo a paramagnetic to ferromagnetic phase transition under tensile strain, however, its origin has been controversial over decades. Some experimental evidence shows that stress leads to the reduction of valence state of cobalt ions and produces spin state transition. Other researchers believe that the stress-induced nano-domain structure will present a long-range ordered arrangement of high spin states, which is the main reason for the ferromagnetism of cobalt oxide films. In this review, we concludes a series recent research progress in the strong correlation between spin and lattice degrees of freedom in cobalt oxide thin films and heterojunctions. The reversible spin state transition in cobalt oxide films are induced by structural factors such as thin-film thickness, lattice mismatch, crystal symmetry, surface morphology, interfacial oxygen coordination, and oxygen octahedral tilt by keeping valence state of cobalt ions unchanged, resulting in highly regulated macroscopic magnetism. Furthermore, researchers used atomic-level precision controllable film growth technology to construct single cell layer cobaltite superlattices and achieved ultra-thin two-dimensional magnetic oxide materials through efficient structure regulation. These series of advances not only clarified the strong coupling between lattice and spin order parameters in the strongly correlated electronic system, but also provided excellent candidates for the realization of ultra-thin room temperature ferromagnets that required for oxide spintronic devices.