Abstract: Investigations ofstall precursors in axial flow compressors are always highlightsof the studies of unsteady turbo-machines flow from a viewpoint ofactive control. Despite extensive researches, many aspects ofstall precursors still remain unresolved. This paper reviewstheoretical models, experimental investigations and mechanismexplorations on the stall precursors in the axial-flowcompressors. Major issues of the stall precursors in the axialflow compressors are concentrated on detecting methods in low andhigh speed environments, the types of the stall precursors, thefluid dynamic mechanism of the stall precursors, etc. An inherentrelation between complex end-wall flow behaviors and the stallprecursors was discussed. Meanwhile, recommendations were made forfuture research, i.e, systematical investigation on influentialfactors of the stall precursors, new types of the stall precursorsin high-speed compressors, underlying fluid dynamic mechanisms ofthe stall precursors and the relationship with design andoperating parameters of the axial flow compressors.