The invention provides a method for controlling a four-propeller thruster of an underwater robot. The real-time position of a three-dimensional rocking bar is detected by an upper computer of the underwater robot and converted into corresponding parameters, and the parameters are sent to a lower computer through 485 communication; after control information sent by the upper computer is received by the lower computer, three-dimensional movement parameters up_dow, fro_bac and lef_rig of the three-dimensional rocking bar are judged, the strength and the direction of the thrust of four propellers are controlled according to order parameters of the tree-dimensional rocking bar, and therefore underwater motion of the underwater robot is controlled, wherein the lower computer controls the underwater robot to float and submerge through judgment of the first dimensional motion parameter, and the underwater robot is controlled to move forwards linearly, move backwards linearly, turn left, turn right, move forwards in the front left direction, move forwards in the right front direction, move backwards in the rear left direction and move backwards in the rear right direction through judgment of the second dimensional motion parameter and the third dimensional motion parameter, the control accuracy and the control efficiency of the underwater robot are effectively improved, and the operation requirement of an operator is well satisfied.