Abstract: To aim at structure modal parameter identification,a method based on a sequence of 2D images was proposed．Chose certain feature points from the object whose modal parameter need to be identified．Factorization method was employed on the image streams taken by CCD camera to solve structure from motion problem and obtain motion track of each point．Eigen-system realization algorithm (ERA) was used to identify modal parameter of structure．Especially when the measure equipment,that is CCD camera was disturbed,it can separate disturbance through image streams and get structure motion parameter,so that the identification result was ensured．A simulation model of cantilever beam under disturbed measurement environment was analyzed．It shows that the first five frequencies of the beam coordinating well with the ANSYS calculation result,which offers high significance to the dynamic characteristic identification using optic images in project programs．