The　applied　light　and　electric　field　can　adjust　the　resistance　of　lanthanide　manganese　oxide thin　films　under　certain　conditions.We　study　resistance　and　lattice　structure　properties　of　LaMnO₃(LMO) film，which　is　grown　on　a　SrTiO₃(STO)substrate　and　performed　diverse　properties　for　different　conditions. The　film's　resistance　does　not　change　significantly　with　the　applied　voltage　when　it　is　not　illuminated　by　a laser　beam.However，when　the　film　is　illuminated　by　a　laser，the　resistance　varies　when　the　applied　gate voltage　changes.We　use　X-ray　diffraction (XRD)method　to　observe　STO　substrate's　lattice　structure　change.We　have　found　that　when　the　electric　field　is　strong　enough，light　increased　oxygen　vacancies'mobility and　enhanced　the　interface　polarization　which　expands　the　lattice　of　STO.