The optical and physical properties of N-face AlGaN-based ultraviolet light-emitting diodes (UV-LEDs) are investigated numerically and compared with Ga-face AlGaN based UV-LEDs. A composition-varying AlGaN electron blocking layer (EBL) is introduced in the N-face AlGaN UV-LEDs. Detailed analysis has been carried out on the electroluminescence spectra, power-current performance curves, energy band diagrams, carrier concentration and radiative recombination rate. The calculated results demonstrate that theN-face UV-LED with composition-varying AlGaN EBL reveals enhanced performance than that of the Ga-face UV-LED with the same structure.