The invention discloses a laser detection apparatus for steam turbine pre-twisted blades. The laser detection apparatus comprises a first slide rail and a second slide rail. A blade detection unit is arranged on the ground between the first slide rail and the second slide rail and comprises a group of blade shaft support seats mounted on the ground. A blade shaft is mounted between the blade shaft support seats and is provided with columns of steam turbine blades to be detected. A first mechanical arm is mounted on the moving guide frame of the first slide rail, and is provided with a laser range finder at the end portion. A PLC control center acquires slit positions of the steam turbine blades in the image data. A second mechanical arm is mounted on the moving guide frame of the second slide rail and is provided with a detection feeler gauge which is used for detecting the slit positions of the steam turbine blades under the control of the PLC control center.