Abstract Due to the complex matrix characteristic of sludge samples, the research on three wet digestion systems and the conditions of reducing agent, and carrier flow was carried. The experiment conditions of HNO3-HClO4 wet systems, namely 5% HNO3 carrier flow, 0. 1% NaBH4 reducing agent, and acidity medium of 5% HNO3 + 0.05% K2Cr2O7 mixed solution, e tc. were finally determined to measure the trace mercury in sludge samples. This recommended method has many advantages, such as accurate and quick detection and simple operation. The determination limit is 0. 06 microg.L-1, and the relative standard deviation for 11-time determination of the solution containing 4.0 microg.L-1 Hg is 2. 0%. This method for trace mercury in sludge samples by hydride generation-fluorescence (HG-AFS) can be widely used.