A new method combined aperture by in plane scanning laser sheet for reducing speckle in laser sheet 3 D sensing is suggested. Scanning the laser sheet within the sheet plane, a dynamic speckle field is shifted on the image lens of CCD camera. Image speckel is occurred on the image plane of CCD, the time integration of the CCD equals to averaging of the image speckle. So the speckle noise is reduced. This method is similar to the moving aperture within a "combined lens" on the image lens, which is larger than the actual aperture. An analytical description is presented and verified experimentally.