Aiming at the problems of fast acid-rock reaction rate，short effective penetration distance and excessive dissolution near the wellbore in conventional acidizing of low-permeability carbonate reservoirs，in this paper，an acid-in-oil-in-water （A/O/W） multiple emulsified acid system was developed to achieve sustained-release and long-distance stimulation of reservoirs. The multiple emulsified acid system was constructed with white oil as the oil phase，compounded hydrochloric acid and acetic acid as the acid phase，Span 80 as the internal-phase emulsifier，and OP- 10 and water as the external aqueous phase，with emulsion stability adopted as the evaluation index. The formulation and preparation parameters were systematically optimized by investigating factors including oil-acid ratio，acid composition，type and concentration of emulsifiers，shear emulsification speed and emulsification time. Its sustained-release performance and acid stimulation effect were evaluated through high-temperature stability test，centrifugal stability test and core flooding experiment. The results indicated that the optimal formulation consisted of an oil-to-acid ratio of 5 ∶ 2，0 . 4 % Span 80 as the internal emulsifier，0 . 2 % OP- 10 as the external emulsifier，and a mixed acid solution containing 5 % hydrochloric acid and 5 % acetic acid. The optimal preparation conditions were a shear speed of 15 000 r/min and an emulsification time of 3 min. Under these conditions，the prepared multiple emulsified acid exhibited a uniform droplet-size distribution and an intact interfacial film，leading to the lowest acid separation ratio and the highest stability under both high-temperature and centrifugal conditions. Core flooding experiments showed that the system maintained a complete A/O/W structure with a pH value of approximately 6 in the near-wellbore zone （0 — 20 cm） . It gradually demulsified with the increase of injection distance and released a large amount of acid at a depth of 60 — 80 cm，realizing sustained release and effectively extending the action distance of acid. The A/O/W multiple emulsified acid prepared in this paper possesses both high stability and sustained-release characteristics，which can provide technical support for acidizing stimulation and production enhancement of low-permeability carbonate reservoirs.