Lattice　expansion　in　hybrid　halide　perovskite　directly　affects　its　photoelectric　properties　and　the　stability　of　perovskite-based　optoelectronic　devices,　which　was　certified　also　to　closely　connect　with　relevant　inducing　mechanisms.　From　the　perspective　of　carrier　relaxation　dynamics　and　dielectric　properties,　we　report　the　results　employing　ultrafast　time-resolved　transient　and　steady-state　reflectivity　technology　to　diagnose　the　lattice　expansion　occurring　in　bulk　hybrid　perovskite　MAPbI(3)　during　continuous　illumination　and　directly　heating,　respectively.　Upon　continuous　illumination　at　a　constant　temperature,　there　were　no　evident　structural　changes　in　MAPbI(3),　but　in　the　condition　of　naturally　temperature　changes,　the　lattice　expansion　can　be　induced　by　continuous　light　illumination　and　is　consistent　with　the　effect　of　heat-inducted　expansion.　The　present　results　are　based　on　the　physical　mechanism　that　the　change　of　the　electronic　structure　caused　by　lattice　expansion　leads　to　the　change　of　the　dielectric　properties　in　MAPbI(3)　and　sequentially　to　the　change　of　light　reflectivity.