An ultraviolet (UV) AlGaInN light-emitting diode (LED) with 370 nm emission is demonstrated. At room temperature (RT) UV power of 0.8 mW at 20 mA with 3.6 V operation voltage is achieved. It provides 4 mW output when driven at 125 mA under continuous-wave (CW) operation. Qualitative optimization of the Al composition in the AlGaN electron-block layer and the quaternary AlGaInN quantum well (QW) number of the UV LED is also investigated in this study. The numerical results fit with the experimentally demonstrated output performance of our AlGaInN UV LED. We find that the UV AlGaInN LED can provide better output characteristics when the Al composition in the AlGaN electron-block layer is in the range 19-21% and the AlGaInN QW number is in the range 5-7 by reducing the electron leakage current.