Graphitic carbon nitride and its nanocomposites with other functional species are attractive light-sensitizers, especially for the development of new opto-electrical devices and photocatalysts in terms of persistant organic pollutants degradation. Herein, oxidized g-C3N4 (O-C3N4) rich in hydroxyl and carboxyl functional groups, was selected as a support to bind with multiporphyrin arrays via a layer-by-layer assembling process, using PdCl42- as connectors and 5,10,15,20-tetra(4-pyridyl)-21H, 23H-porphine (TPyP) as linkers. The as-obtained multi-porphyrin@g-C3N4 nanocomposites exhibited dramatic photocatalytic visible-light degradation of Rhodamine B and phenol. The experimental results demonstrated that TPyP was not just as the photosensitizer, but also a charge promotor to retard the recombination of the excited electrons and holes of g-C3N4. Both the holes and O-2(center dot-) are main oxidative species of multiporphyrin@ g-C3N4 nanocomposites for photodegradation under visible light irradiation. Finally, the possible charge transfer mechanism of enhanced photocatalytic activity was proposed.