The invention belongs to the digital high-definition video compression coding and decoding technology field and especially discloses a rapid algorithm suitable for intra-frame prediction block size division of an HEVC standard. In the HEVC standard, an intra-frame prediction mode can be selected and used to carry out video compression. Sizes of intra-frame prediction units have five types which are 4*4, 8*8, 16*16, 32*32 and 64*64. During coding, a proper block size division mode according to an image is selected. The algorithm in the invention carries out processing based on a maximum coding unit. Firstly, gradient calculating is performed: the gradient calculating is performed on a point which can be operated in a LCU; secondly, all the point gradient calculating results in a prediction unit block scope are added so as to acquire image complexity of the prediction unit; finally, block size division is performed according to each prediction unit complexity value obtained through calculating. Through the rapid algorithm, an optimal block size division mode of the prediction unit is acquired so that an intra-frame prediction block size division process is accelerated.