In the traditional ray tracing algorithm on the basis of linear traveltime interpolation (LTI),rays trans-mitting through multiple grids may cause error accumulation due to the linear assumption.When the algorithm isapplied to the computerized tomography for industrial flaw detection,the materials to be detected often become acollection of the background and a small amount of defect areas.In order to reduce the accumulative error in thisapplication,a new ray tracing algorithm on the basis of boundary LTI is proposed.In this algorithm,nodes are in-serted on the boundary of different areas to determine rays' refractional angle and to further reduce the accumulativeerror,and the multidirectional cyclic scanning is used for reference to guarantee the ray path when rays transmit ina reverse direction.Simulated results show that the proposed algorithm is superior to the traditional LTI algorithmand the cross- scanning LTI algorithm due to its high traveltime computing accuracy and ray path- tracing accuracy.