The invention discloses a lightweight composite material supporting structural component for a track traffic tunnel and a mounting method of the lightweight composite material supporting structural component. The structural component comprises a lining reinforcement band support fixed to the inner surface of a tunnel segment, a carbon fiber composite section lining reinforcement band pasted on the lining reinforcement band support and a cement paste injection pipe joint, the reinforcement band is filled with cement paste, and the cement paste injection pipe joint is used for injecting the cement paste into the carbon fiber composite section lining reinforcement band. The carbon fiber composite section lining reinforcement band comprises an external supporting shell, a soft carbon fiber connecting mesh in the space of the external supporting shell and a flexible carbon fiber braided band wrapping the outer portion of the external supporting shell, and the external supporting shell is an elastic hard carbon fiber composite plate. The structural component does not intrude in the train running safety boundary, a tunnel lining overlaying layer is effectively formed, a tunnel is reinforced fast under the severe condition that allowed maintenance time is short, the overall rigidity and bearing capacity of the tunnel are greatly improved, and occupied space is small.