In this work, the ternary Bi2O2CO3/Fe2O3/BiOCl (BOC/Fe2O3/BiOCl) and binary Fe2O3/BiOCl heterojunctions are synthesized by an in-situ hydrothermal method. It is found that the addition amount of FeCl3 has a great influence on the formation of multiple heterojunctions. The XRD and HRTEM results illustrate that the formation of multiple heterojunctions. At FeCl3: BOC = 0.1–0.8:1 (molar ratio), the BOC/Fe2O3/BiOCl ternary heterojunction has formed (S1 0.1Fe-BOC-S5 0.8Fe-BOC). At FeCl3: BOC = 1: 1 and 2.5: 1 (molar ratio), the Fe2O3/BiOCl binary heterojunction has formed (S6 1Fe-BOC, S7 2.5Fe-BOC). Besides, under ultraviolet light irradiation (λ < 400 nm), the photocurrents of S4 0.7Fe-BOC, S5 0.8Fe-BOC, S6 1Fe-BOC and S7 2.5Fe-BOC are 4, 3, 6 and 5 times higher than that of BOC, respectively suggesting the greatly improved charge transfer and separation efficiency. Under ultraviolet light irradiation (λ < 400 nm) within 20 min, ∼40% of rhodamine B (RhB) are photodegraded by S4 0.7Fe-BOC and S5 0.8Fe-BOC, ∼65% of RhB are photodegraded by S6 1Fe-BOC and S7 2.5Fe-BOC. While 8% and 2% of RhB are photodegraded by S1 0.1Fe-BOC and BOC within 20 min, respectively. The apparent reaction kinetic rate constant (ka) for S1 0.1Fe-BOC (0.024 min−1), S4 0.7Fe-BOC (0.082 min−1), S5 0.8Fe-BOC (0.086 min−1), S6 1Fe-BOC (0.127 min−1) and S7 2.5Fe-BOC (0.093 min−1) are 2.7, 9.1, 9.6, 14.1 and 10.3 times as high as that of BOC (0.009 min−1), respectively. The higher photocatalytic activity of the composite is mainly due to the heterojunction formation, which efficiently improves charge separation and favors the generation of superoxide radical (O2–) and hydroxyl radical (OH). This work provides a simple in-situ hydrothermal method to fabricate multiple heterojunctions with the obviously boosted photoactivity.