Ideality factor can reflect the current, the carrier leakage, and the phenomenon of non-radiative recombination in light-emitting diode (LED). For the problem of ideality factor from current report about GaN-based LED, the value of ideality factor n is calculated by using the I-V curve fitting of high voltage LED. And the relationship between the ideality factor and the number of units is series in 12, 19, 51 and 80 V GaN-based high-voltage LED are discussed. In addition, the relationship between ideality factor and spectral half width (FWHM) is analyzed, and the impact of current crowding effect on the ideality factor is also studied. Results show that the ideality factor n increases nearly linearly with the number of units in series, indicating that the ideality factor n of high voltage LED is composed of its series units. It is a valuable result for understanding the ideality factor of GaN-based high voltage LED.