The carriage positioning of excavator in three-dimensions (3-D) is the precondition of the robotic excavator starting roboticized works. In order to get the carriage position of excavator in three-dimensional space, angle sensors of such joints as bucket, arm, boom, and boom deflection are brought to bear. At the same time, a 2D-inclination sensor is introduced to check the list and pitch angles of the platform, and a rotatory angle sensor is introduced to check swing angle of the platform. And a laser receiver was mounted on the arm to measure the relative height of the arm to the laser beam from ground sender. Then the kinematic model is established, the coordinate transformation matrix of carriage positioning is formulated, and the height of the body relative to the ground is gotten. As a result, the coordinate transformation matrix of the bucket relative to the ground and the digging depth are formulated. That makes the excavator orient bucket precisely and set excavation depth exactly, and make automotive elaborate excavation come true.