Reasonable use of cocatalyst plays vital role for the enhancement of photocatalytic H-2 evolution from water splitting. Herein, a novel ternary MoS2/CdS/rGO nanocomposite was creatively synthesized by facile one-step hydrothermal method through densely overspreading MoS2/CdS eutectic cluster nanospheres on the edge of rGO nanosheets. The constructed photocatalyst system shows excellent visible-light-driven photocatalytic performance and good stability, and the corresponding H-2 evolution rate is nearly 22 times higher than that of the original CdS for solar water splitting. The photocurrent response test and photoluminescence (PL) spectra indicate that the as-prepared nanocomposite possesses the efficient spatial charge separation as well as faster electron transfer between CdS and MoS2 through the conductive network of rGO. For interpreting the excellent performance, two transfer routes of excited electrons have been put forward to describe the reasonable redistribution of surface electrons under the "transfer" effect of MoS2 and "bridge" effect of rGO in this ternary system. This work provides a new scenario for the reasonable use and synthesis of the low cost and efficient MoS2 cocatalyst, which also show reference value of rational design and preparation of high performance photocatalysts.