Formic acid (FA) is an ideal carrier for hydrogen (H2) and carbon monoxide (CO). Thus, photocatalytic reforming of FA is considered a promising energy conversion method for producing solar fuels and valuable chemical feedstocks to achieve the carbon-neutral goal. However, the application of FA photocatalytic reforming has been restricted by the low efficiency and relatively fixed selectivity due to limited knowledge about the reaction mechanism. Herein, we show 1D CdS/2D W2N3 heterojunction as an efficient photocatalyst for photoreforming of FA with tunable selectivity to realize the conversion of products from H2 to syngas under simulated sunlight. Widely tunable CO:H2 ratios between 0 and 2.18 along with a record-high apparent quantum yield (AQY) of 61.00% (H2) and 76.84% (syngas) at 420 nm have been demonstrated. Both theoretical investigation and experimental results show that intrinsic N vacancies and spatially separated active sites are vital factors in achieving tunable selectivity. This work provides a brand-new strategy and insightful information to construct a noble-metal-free photocatalytic system for efficiently reforming of FA with tunable selectivity.