The construction of the cable tunnel underneath Qinhuai River of a transformer substation at dock is a great challenge,as a result of high water table,soft ground under riverbed,deep friction piles in embankment,restricted construction methods,embankment protection during tunneling and high requirement of tunnel drainage.Finally,shield machine was selected for the cable tunnel construction after an overall comparison of underwater tunnel construction methods and analysis of the influences of riverbed erosion and other factors on tunnel cover.In addition,pile foundation underpinning and grouting are proposed for embankment reinforcement before tunneling after analysis of embankment stability and safety;and a tunnel drainage scheme is draw up through comparison of practicability and safety,including single slope drainage and pumping station in launching shaft.The smooth construction of the cable tunnel shows that the selected construction method and embankment reinforcement measures are safe and reliable,and the tunnel drainage scheme is effective and practical. 