The checking and accepting standards of Hy drological Data Acquisition System (HDAS) const ruct ion vary with its work mode.The analytical methods of HDAS reliability could be different under different structures.The reliability of the built-up of HDAS in Taihu Basin is discussed in this paper by means of probability analysis.The reliability is better to measure the polling-answering system with memory than the accessible rate of a monthly average, and the reliability has been influenced by the sy stem structure.It is of great significance that the reliability of HDAS is studied by the probability-stat istics on the draf t of checking and acceepting standards of the system construction and the st ructure design of HDAS.