The performance of continuous composite deck slab (CCS) strengthened with unidirectional carbon fibre-reinforced polymer (CFRP) laminate in the hogging region was investigated in this study, where the CFRP worked as an external reinforcement in the concrete tension region. Four specimens of CCS that consisted of two equal spans were tested experimentally under static loads after strengthening with CFRP laminates of varying lengths. The test results confirmed that the hogging moment capacity of the CCS was improved significantly when the CFRP length was increased. However, CFRP debonding failure occurred in all strengthened specimens, and increasing the CFRP length did not totally prevent the debonding failure from occurring, although it did delay this failure somewhat. The CCS specimens absorbed more energy when strengthened with the CFRP laminates.