Advanced marine structures are in demand for the efficient acquisition of marine resources. The trussed tubular hybrid structure incorporating composite members such as concrete-filled steel tubes (CFST) exhibits excellent structural performance and easy-to-take anti-corrosion measures, indicating its great potential to be utilized in floating structures such as offshore platforms for wind turbines. Applying modular connection technology to trussed tubular hybrid structures effectively improves the on-site construction speed, and reduces the impact of harsh marine environments on the construction quality. In this study, three types of novel inter-modular self-locking connection configurations with better sealing performances are proposed, which would be suitable for marine modular trussed tubular hybrid structures. The connection design is optimized through pre-splicing tests, and the mechanical performance of the connection under axial tension is then revealed through experimental tests. The test results demonstrate that the self-locking connection exhibits excellent tensile behaviour, where the pressing blocks and the shear keys in the connection can jointly resist the tensile force as a whole. Fracture at the upper plate of the sliding groove is identified as the typical failure mode. It is found that increasing the thickness of the upper plate at the sliding groove can effectively improve the tensile strength of the proposed connection.