The increase in anthropogenic CO2 concentration is one of the main challenges of the mankind. CO2 sequestration is expected to become one of the world’s most significant technologies for reducing carbon emissions. Among the sequestration methods, Oceanic Carbon Capture, Usage, and Storage (OCCUS) offers the highest capacity for storage in a shorter period and is safer in terms of CO2 retention compared to geological sequestration methods. CO2 can be injected into oceans at various depths and forms (phases), including liquid, solid, gas, and supercritical. Marine carbon sequestration is an emerging carbon sequestration technology with excellent development potential and known advantages. It is one of the essential measures to achieve large-scale carbon emission reduction and has broad application prospects. Therefore, this paper systematically focuses on the basic principles, technical status, monitoring and evaluation, and environmental impacts of Ocean CO2 Direct Injection and Storage (OCS). Moreover, we elaborate on the efficient ways of implementing CO2 injection, CO2 leakage detection, prevention and remediation technology, and ecological aftereffect of ocean carbon sequestration.