The invention discloses a method for measuring relative positions of a propeller and rudder blades of a vessel. The method is used for an integrated hanging rudder which does not need boring and processing, of a rudder system, and specifically comprises the following steps of firstly, fixing an upper sliding assembly on a steering engine deck, fixing a lower sliding assembly on the lower end surface of a rudder stock cylinder, and adjusting the upper sliding assembly and the lower sliding assembly to enable a steel wire to be located in a central axis of the rudder stock cylinder, wherein thesteel wire can express a rudder system center line; and then finding out a target center of a head reference target and a target center of a tail reference target by a tacheometry, and finding out a straight line by a collimating telescope, wherein the straight line sequentially passes through the target center of the tail reference target and the target center of the head reference target, and isa shaft system center line. According to the method disclosed by the invention, the relative positions and the relative distance between the propeller and the rudder blades are measured by using therudder system center line and the shaft system center line as the references; a stern shaft pipe is bored and processed according to measurement data, so that the shaft system center line is solidified, and the situation that regulated requirements of the relative positions of the propeller and a rudder are met is guaranteed.