The dendrite growth and the associated misorientation evolution on the platform base of a single crystal in-vestment casting were investigated. It was found that the long secondary dendrite arm (LSDA) grew through the whole platform, and a convergent boundary of dendrite arms (CBDA) formed simultaneously between the corresponding branched arms and the extended secondary arms from the blade zone. The corresponding or-ientation measurement confirmed that the misorientation of dendrite arms between the two sides of the CBDA monotonically increased from 5.9° at one platform edge to 33.5° at the other platform edge. Additionally, the LSDA dendrite deformation was also identified by the accumulated misorientation within the LSDA dendrite core. Furthermore, it was deduced that the increased misorientation along the CBDA was caused by the LSDA dendrite deformation, and the reason of LSDA dendrite deformation was further discussed based on the asso-ciated strain distribution around the LSDA. Because of a 33.5° misorientation along the CBDA, it was indicated that the dendrite deformation might be the formation mechanism of high angle boundary.