In many syntectonic granitoids, micro_intergrowth, a kind of micrograined mineral aggregates different from mylonization matrix, has been found. It fills in the seams and triple junction channels among the larger mineral grains, generally with a content of 2%~6% in the rocks. It consists mainly of micrograined quartz, albite, potassic feldspar, myrmekite, etc.,and can be divided into two types: granular and myrmekitic intergrowth. In composition, it is just like a late crystallized product of granitic magma. According to the characteristics of its occurrence, composition, petrography and the experimental conclusion that the dominant deformation mechanism will change into dislocation creep when the melt content in the rock is lower than 3%~5%, it is suggested that micro-intergrowth is a crystallization product of a small amount of residual melt (about <3%~5%) in rocks under strong stress. So it can be considered generally as a microstructure marker of synkinematic crystallization in intrusions.