Engineering defects and/or amorphous shells is a promising strategy to improve the photocatalytic efficiency of the oxide materials. In this work, we developed a safe and easy magnesiothermic reduction method to prepare surface-disordered hybrid nanocomposites, taking Zn2SnO4/SnO2 hollow microboxes as an example. Our results demonstrate that the reduction treatment can successfully introduce oxygen vacancies and amorphous shells in the pristine Zn2SnO4/SnO2 sample, causing narrowing of the band gap and reinforced solar light harvesting. Moreover, the Mg-reduced Zn2SnO4/SnO2 heterojunction photocatalysts exhibit enhanced sunlight-driven hydrogen production activity and degradation performance of the organic pollutant. This strategy may disclose a new avenue for improving photocatalytic performance of defect-engineered heterojunction composites toward broader applications.