The invention belongs to the technical field of computational mechanics, and relates to a method for obtaining complete developing flowing boundary conditions of a channel inlet.The method comprises the steps that firstly, a segment of a plane channel is additionally arranged in front of an original channel inlet to obtain a modified channel; secondly, on the basis of a set monitoring point, whether the length of the additionally arranged plane channel meets the requirement that an original channel inlet boundary achieves complete developing flowing speed distribution or not is judged, and if not, adjusting is performed; whether the modified channel inlet boundary turbulence quantity meets the requirement that the original channel inlet boundary achieves complete developing flowing turbulence kinetic energy distribution or not is judged, if not, adjusting is performed, and if yes, the method for obtaining the complete developing flowing boundary conditions of the channel inlet is completed.According to the method, errors brought by experimental data point collecting and curve fitting performing can be effectively decreased, the operation process for obtaining complete developing distribution is simplified, and the complete developing flowing inlet boundary conditions can be quickly and effectively obtained at the channel inlet.