Morphology modulation of photocatalyst has been demonstrated to be a crucial strategy for improving the catalytic performance in solar energy conversion system. Here we systematically investigated the influence of the solvent-dependent morphology evolution of Zn2GeO4 phase on the photocatalytic efficiency of the as-prepared g-C3N4/Zn2GeO4 composites. The morphologies of Zn2GeO4 were rationally tuned from flower-like nanosheets to length-controllable nanorods, and microclusters assembled from microrods through regulating the solution polarity of different organic solvents. Accordingly, the Zn2GeO4 sample prepared in ethylene glycol (EG) with long rod-like morphology and integrated with g-C3N4, abbreviated as g-C3N4/Zn2GeO4(1:1)-EG, exhibited the best visible-light absorption ability and the highest efficiency. The synergetic effect of the long rod-like Zn2GeO4 phase with many exposed (110) crystalline facets and g-C3N4 accelerates the separation and interface transportation of photoexcited charge carriers, as confirmed by photocurrent measurements. The MB degradation mechanism was also proposed to clarify the charge-transfer process and the improved photodegradation activity. This study offers an experimental basis for understanding the significance of morphology control on rational design of photocatalysts with improved performance.