This application provides a method for determining a coding tree node split mode and a coding device. The method includes the step of determining a non-split based coding cost for coding a current image area corresponding to the current node and determining a binary tree split based coding cost for coding the current image area. The method further includes determining, based on the non-split based coding cost and the binary tree split based coding cost, whether a triple tree split based coding cost for coding the current image area needs to be obtained. If the triple tree split based coding cost needs to be obtained, a triple tree split is performed on the current node. The method then determines a split mode of the current node that corresponds to a minimum coding cost.