The invention relates to the field of sizing agent detection, in particular to a sizing agent soaking detection method. The sizing agent soaking detection method comprises the following steps that 1, a sizing agent to be detected is detected, wherein a solution of the sizing agent to be detected is prepared, a paperboard is soaked in the solution of the sizing agent to be detected, the paperboard absorbs the solution of the sizing agent to be changed into a wet paperboard, the redundant solution of the sizing agent to be detected is removed, the half-dried paperboard is dried to obtain a board to be detected, and the board to be detected is detected to obtain detection data; 2, the solution of the sizing agent to be detected in the step 1 is replaced with a standard sizing agent solution, detection is performed for multiple times according to the steps in the step 1, and standard range data is obtained; 3, the detection data is compared with the standard range data to obtain a conclusion. According to the sizing agent soaking detection method, sizing agent performance testing is completed in a laboratory by simulating actual production, therefore, the phenomenon that the sizing agent to be detected is directly loaded onto a machine for production detection is avoided, and the detection and production cost is greatly lowered.