OBJECTIVE： To prepare Activated carbon N-acetylcysteine microcapsule （ACNAC）， and to optimize preparation technology. METHODS： ACNAC was prepared by emulsion cross-linked method using biodegradable material gelatin as capsule wall material. Using comprehensive evaluation index of drug-loading amount， entrapment rate and particle size distribution percentage （the percentage of 80-140 μm particle） as index， drug-loading ratio， amount of gelatin， mixing speed and the amount of emulsifier as factors， single factor test and orthogonal test were used to optimize formulation technology. The technology was validated and distribution of particle size of ACNAC was determined. RESULTS： The optimal formulation technology was as follows as drug-loading ratio 1 ∶ 1， gelatin 15％， emulsifier 2.0％， mixing speed 1 000 r/min. Average drug-loading amount of 6 batches of ACNAC was 15.9％ （RSD＝1.21％）， average encapsulation efficiency was 78.1％ （RSD=1.11％） and average particle size distribution percentage was 81.9％. CONCLUSIONS： ACNAC is prepared successfully， and formulation technology is reasonable and feasible.