The synthesis of nanomaterial on porous materials and use of their porous structure for oil-water separation and oil absorption underwater at normal temperature and pressure are a very significant process, which has attracted wide attention. In this paper, dahlia-like Co3O4 nanoparticles was synthesized on the surface of porous nickel foam by hydrothermal reaction. After modification with heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane (FAS-17), the as-prepared sample surface could obtain good oleophobicity and excellent superhydrophobicity with high contact angles and low sliding angles. Furthermore, the as-prepared superhydrophobic composite had low adhesion to water and light oil, and could be subjected to simple and effective oil-water separation (including three light oil and one heavy oil) at normal temperature and pressure. Due to the magnetic properties of nickel foam, underwater oil absorption experiment was carried out by magnetic traction, which could achieve a perfect oil absorption effect. In addition, the comprehensive use of unmodified and modified Co3O4/nickel foam at the end of tube can quickly and efficiently carry heavy oil (trichloromethane)-water separation and collection. Therefore, the as-prepared dahila-like Co3O4 on nickel foam not only has good application value in oil-water separation, but also has excellent potential in underwater oil absorption.