The development of assistive lower-limb exoskeletons gains prominence for human load-carrying augmentation. Hydraulic transmission has attractive hydrostatic features and lower inertia at the end of human limbs. However, few hydraulic lower-limb exoskeletons were developed with low energy consumption and light weight. In this article, we introduce HyExo, a quasi-passive hydraulic exoskeleton that is built on a lightweight rotary cage valve (RCV) block with a fast response and low energy consumption of 1.55 W. Based on the RCV block, we propose an optimization-based regulator for joint energy distribution to harvest and release the hydraulic energy among joints during the stance phase. The interaction force model and control of the novel nonanthropomorphic structure are presented and evaluated. The load-supporting effect was investigated and validated through human subject experiments. The results show that with an assisting fluid pressure of 2.5 MPa, HyExo can transfer a mean force of 237 N to the ground. Meanwhile, the impact of wearing HyExo on gait is analyzed. The metabolic expenditure test shows that HyExo can slow the increasing rate in metabolic cost as load increases. Compared with a regular backpack, walking with HyExo to carry 30 kg of weight reduces wearers' metabolic energy expenditure by 7.8%.