Porous graphitic carbon nitride was synthesized by controllable thermal polymerization of urea in air. Their textural, electrical, and optical properties were tuned by varying the heating rate. The presence of proper residual oxygen in carbon nitride matrix had enhanced light absorption and inhibited the recombination of charge carriers. Furthermore, the MoS2 nanosheets were coupled into the carbon nitride to form MoS2/C3N4 heterostructures via a facile ultrasonic chemical method. The optimized MoS2/C3N4 heterostructure with 0.05 wt % MoS2 showed a reaction rate constant as high as 0.301 min(-1), which was 3.6 times that of bare carbon nitride. As analyzed by SEM, TEM, UV-vis absorption, PL and photoelectrochemical measurements, intimate contact interface, extended light response range, enhanced separation speed of charge carriers, and high photocurrent density upon MoS2 coupling led to the photocatalytic promotion of the MoS2/C3N4 heterostructures. In this architecture, MoS2 served as electron trapper to extend the lifetime of separated electron hole pairs. Meanwhile, the accumulated holes on the surface of carbon nitride oxidized the organic dye directly, which was a predominant process in the photodegradation of organic pollutants in water treatment. The promotional mechanisms and principles reported here would have great significance in heterogeneous photocatalysis.