We propose two composition-graded quantum barriers (QBs) to improve the performance of AlGaN-based deep ultraviolet laser diodes (DUV-LDs). The optical and electrical properties of three LDs containing conventional QBs, graded increased QBs, and graded decreased QBs were numerically investigated. It was found that the LDs with graded decreased QBs significantly improved the carrier injection efficiency, raised the carrier concentration in the active region, reduced the carrier leakage, and enhanced the stimulated recombination rate of the LDs. Simulation results showed that, at an 80-mA injection current, the threshold current and threshold voltage were reduced to 29.5 mA and 4.78 V, respectively. The slope efficiency was improved to 2.52 W/A, and the electro-optical conversion efficiency was increased to 52.2%. Compared with the conventional structure of LDs, grading the QBs with decreasing Al-content improved the performance of the LD remarkably, which is essential for the development of DUV-LD.