To explore lightning properties, a near-infrared afocal continuous zoom laser beam expanding system with large zoom ratio was designed to simulate lightning spot elements with different sizes for the lightning scene in a laboratory. On the basis of Gaussian geometric method, the overall dimensions of the system was calculated and the diameters and focal powers of lenses were determined reasonably. By using ZEMAX optical design software, optical structural parameters of the system were optimized, then total performance of the system was analyzed and evaluated. As the results, the system shows a 13X beam expansion ratio and excellent emitting beams with higher energies, uniform spots, and diffraction-free rings, which meets the requirements for simulating lightning properties. Furthermore, the central wavelength of the afocal laser beam expanding system is 777.4 nm, the incident laser beam with a diameter of 1.0 mm is continuously adjustable by a stepper motor and the emitted beam diameter ranges from φ0.8 mm to φ10.6 mm. The beam expanding system has some advantages of fewer lenses, simple structures and smoothly zoom trajectory, and it is suitable for simulating lighting elements with different sizes.