The invention relates to a method for building a CsPbBr3 nanosheet electroluminescent device by chemical vapor deposition (CVD). The preparation method comprises the steps of loading CsBr powder and PbBr2 powder in a magnetic boat 1 according to a mole ratio being (1.85-2.05):1, laying an ITO glass sheet etched with an electrode on a magnetic boat 2, placing the magnetic boat 1 at a middle part of a horizontal tubular furnace, and placing the magnetic boat 2 at one end, near to an air outlet, of the horizontal tubular furnace; and introducing a carrier gas, discharging air in the furnace, introducing the carrier gas, rising a temperature to a heating temperature being 570-600 DEG C of the magnetic boat 1, rising the temperature to a heating temperature being 300-400 DEG C of the magnetic boat 2, and performing deposition to obtain a product. The CsPbBr3 nanosheet device is built on an ITO electrode initially by a simple method, and light emitting under electric injection is achieved. The obtained device has high-efficiency and stable performance and can be applied to a nanoscale photoelectric integrated circuit.