Mode S Second Surveillance Radar (SSR) is very important means for Air Traffic Control (ATC) now and future,all the responding data which the radar receives need parity processing. Bit and confidence declaration is an vital step before error detection and error correction. Based on the commonly used baseline multi-sample algorithm,different conditions are presented and analyzed,the conditions under which error happens are pointed out,and the algorithm in which two statistical variables are added to avoid false declaration. In addition,the moving average method is used to preprocess the sampled data,so as to reduce the influence of noise. The merits the baseline multi-sample technique owes are preserved,and the added computation is small. The declaration veracity is improved,and consequently makes error detection and error correction be facilitated suc-cessfully. Mode S Second Surveillance Radar (SSR) is very important for for Air Traffic Control (ATC) now and future, all the responding data which the radar receives need parity processing. Bit and confidence declaration is an vital step before error detection and error correction. Based on the commonly used baseline multi-sample algorithm, the conditions under which error are are out, and the algorithm in which two statistical variables are added to avoid false declaration. is used to preprocess the sampled data, so as to reduce the influence of noise. The merits the baseline multi-sample technique owes are preserved, and the added computation is small. The declaration veracity is improved, and therefore makes error detection and error correction be facilitated suc-cessfully.