NOVELTY - A methylamine halogenated plumbate compound large-size crystal growing method involves placing halogenated methyl mine in ice water bath, adding aqueous methylamine hydrohalic acid to react to obtain a reaction product, which is rotary-evaporated to obtain methylamine halide precipitate. The precipitate is recrystallized by adding anhydrous ethyl ether and dried to obtain halogenated methyl amine crystal, followed by preparing methylamine halogenated plumbate compound large-size crystal by adding the obtained halogenated methyl amine crystal and lead acetate trihydrate in halide solution.    USE - Method for growing methylamine halogenated plumbate compound large-size crystal that is utilized as electro-optical material, ferroelectric material, OLED material, field effect transistor material or thermoelectric material, and in solar cells (all claimed).    ADVANTAGE - The method enables growing the methylamine halogenated plumbate compound large-size crystal with better light absorption range in the UV-visible light region, better stability, and without deliquescence, in an easy and inexpensive manner.    DETAILED DESCRIPTION - A methylamine halogenated plumbate compound large-size crystal growing method involves placing halogenated methyl mine (CH3NH3X) in ice water bath, adding aqueous methylamine hydrohalic acid to react to obtain a reaction product. The reaction product is rotary-evaporated by rotary evaporator to obtain methylamine halide precipitate. The precipitate is recrystallized by adding anhydrous ethyl ether and dried in vacuum to obtain halogenated methyl amine (CH3NH3X) crystal, followed by preparing methylamine halogenated plumbate compound large-size crystal (CH3NH3PbX3) by adding the obtained halogenated methyl amine crystal and lead acetate trihydrate in halide (HX) solution according to the stoichiometric proportion, stirring and performing clarification of a dissolving liquid by increasing temperature to saturated point. The seed crystal is added, rotated and cooled at a rate of 0.5-2 degrees C/day for 1 month, followed by carrying out crystal growing process, where the halide in the methylamine halogenated plumbate compound and X is chlorine, bromine or iodine. An INDEPENDENT CLAIM is also included for a device for growing methylamine halogenated plumbate compound large-size crystal.