In the preparation of Sn-Pb alloyed perovskite, a large amount of stannous fluoride (SnF₂) additive is often employed to inhibit the oxidation of Sn²⁺ ions. However, excessive SnF₂ deteriorates quality of the film, photoelectric conversion efficiency (PCE) and stability of the device. Therefore, the development of new antioxidants at low doses is essential to achieve high-performance Sn-Pb alloyed perovskite solar cells. In this study, a two-step process was used to prepare Sn-Pb alloyed perovskite film. In the first step, low-dose stannous iso-octanoate (SnOct₂) was introduced to replace SnF₂ to inhibit the oxidation of Sn²⁺. This study showed that the additive could improve the crystallization quality of the film, and the average grain size of the film with SnOct₂ could reach 850 nm while the amount of grain boundaries was reduced. The film with the addition of SnOct₂ still contained 93.5% Sn²⁺ after storage for 7 d in the glove box. And due to the excellent oxidation resistance of SnOct₂, the device with the additional SnOct₂ had a lower defect state density, which was reduced from 7.20×10¹⁵ to 4.74×10¹⁵ cm^-3, inhibiting the non-radiative recombination. In addition, SnOct₂ improved the surface energy levels of perovskite films. Finally, PCE of Sn-Pb alloyed perovskite cell supplemented with 0.030 mmol SnOct₂ reached 17.25%, superior to that of device supplemented with 0.10 mmol SnF₂ (11.63%). After storage in nitrogen for 50 d, more than 70% of initial PCE was still preserved.