The invention discloses a structure laser scanning technology based study method for surface defect of a converted timber. The method comprises the following steps: acquiring 3D structure information of the converted timber; measuring the property parameters of the converted timber; calculating arithmetic average deviation of absolute value of the distance from each point on the profile of the surface, to be measured, of the converted timber, to a center line within the measuring length L range of the surface, to be measured, of the converted timber; acquiring a converted timber image within the measuring length range; determining the surface knurr appearance quality influence coefficient h, the crack position influence coefficient k, the crack length influence coefficient p and the maximum mean square deviation according to the parameters in the converted timber image; creating converted timber appearance quality comprehensive quantization evaluation value Q according to the knurr appearance quality evaluation value Qk, the crack appearance quality evaluation value Qc and the color difference appearance quality evaluation value Qd; and dividing Q into four grades. According to the method, the surface defect of the converted timber can be quickly detected on the basis of detected surface roughness of the converted timber, thus increasing the converted timber surface detecting efficiency as well as improving the detection effect.