Rational design and large-scale synthesis of proton exchange membranes with high proton conductivity are essential for their practical applications in fuel cells and storage devices. Herein, a facile approach to prepare proton conductivity membrane which possessed new proton transport channel was reported. The composite membrane was prepared by in situ sol-gel method using SPEEK as polymer matrix and carbon nitride (g-C3N4-H+) as reinforcing agent. The g-C3N4-H+ is the 2D nanosheet, and also contains a large number of channel, which can provide new approach for proton transfer. Moreover, this structure allows the composite membrane to form more hydrogen bonding networks at its interface as well as internal area, thus improving the proton transfer efficiency. The proton conductivity of the SPEEK/g-C3N4-H+ composite membrane reached 10.86 mS cm−1, which is 3.64 times higher than that of the pristine SPEEK membrane at the temperature of 25 °C.