In this paper, the search strategies in the acoustic layer of the CSR (continuous speech recognition) and the CDM (Chinese dictation machine) are addressed in two aspects, the acoustic recognition unit and the syntax-constrained word search tree. The SKB-FSS (statistical knowledge based frame synchronous search) algorithm and the syntax-constrained WST (word search tree) structure are proposed, they form the TLSN (two-level search network) in the acoustic layer. The statistical knowledge used by the algorithm includes differential state dwell distribution, the feature difference sum and so on, which result in an improvement of 36.6% in CSR. The principles of a modified back-off estimation algorithm and the search algorithms for the N-gram based language models are also introduced. Finally, by integrating the authors' techniques, a Chinese dictation machine engine (CDME) is implemented. A speaker-independent CDM text editor named ST97 and a voice command system named CMD97 are established for personal computers (PCs) based on the CDME.