In this study, NaNbO3 microcubes were introduced during the preparation of Bi2O2CO3 nanosheets to construct a series of NaNbO3/Bi2O2CO3 heterojunctions with varying NaNbO3 content. Their photoactivities for N2 fixation were examined and compared. Results demonstrated that 7.5% NaNbO3/Bi2O2CO3 had the highest photoactivity. The NH3 production rate under simulated solar light is 453.1 μmol L-1 g-1 h-1, representing 2.0 and 3.8-fold increases compared to those of Bi2O2CO3 and NaNbO3, respectively. A comprehensive investigation encompassing the physical and chemical properties of the NaNbO3/Bi2O2CO3 photocatalyst was conducted. Bi2O2CO3 nanosheets were discovered to be distributed on the NaNbO3 microcubes surface. The addition of NaNbO3 exhibited nearly no effect on the photoabsorption performance and specific surface area of the Bi2O2CO3. However, the tight contact between NaNbO3 and Bi2O2CO3 and their appropriate band positions led to the formation of a heterojunction structure between them. The electron drift occurring in the interface region induces the creation of an internal electric field and energy band bending. This facilitates the transfer of photogenerated electrons and holes through an S-scheme mechanism, achieving efficient separation without compromising the redox performance. As a result, the NaNbO3/Bi2O2CO3 composite exhibits exceptional performance in the photocatalytic nitrogen fixation reaction. This study expands the application of S-scheme photocatalysts in the field of N2 reduction and provides insights into the preparation of efficient S-scheme photocatalysts.