Photocatalysis, as a form of solar energy conversion, has considerable development prospects for solving energy exhaustion and environmental pollution. Promoting the utilisation of photocarriers is the key way to enhance photocatalytic activity and quantum efficiency. The g-C3N4 with the width of the band gap responsive to visible light, which is a great concern for researchers, was prepared by thermal decomposition and the insides were stripped from the outer wall and then curled to form the nanotubes (NTs), microtubes and shorten the migration distance of the electrons and holes. To promote the separation of the photocarriers in the g-C3N4, Ag particles are deposited by photoreduction as electron "traps" with surface plasmon resonance (SPR), and an external magnetic field is introduced during the photocatalysis. Under the Lorentz force, the photocatalytic efficiency of the Ag@g-C3N4 NTs is 200% higher than that of bulk g-C3N4, as a result of being able to prolong the life of the photogenerated carriers to bypass the recombination sites.