Apparatuses and methods for detecting multilayer multipass welding trajectory are disclosed. The apparatus includes an imaging component, a first and a second directional light source group, a structured light source and a control and processing component. The imaging component is disposed in front of a welding gun and above a weld pass. The first and the second directional light source group are disposed symmetrically above the weld pass and at two sides of the weld pass. The structured light source is disposed above the weld pass. The control and processing component is configured to control the imaging component to capture an image of the workpiece surface separately when the first directional light source group, the second directional light source group or the structured light source emits the light to the workpiece surface and to obtain a multilayer multipass welding trajectory according to the images.