Embodiments of this application disclose a signal processing method and a related apparatus, to estimate a passive intermodulation (PIM) signal strength. The method in embodiments of this application includes: obtaining first downlink signal data corresponding to each of N cells in a preset bandwidth resource scheduling solution. Then, first characteristic data corresponding to each piece of the first downlink signal data is determined. Then, a first passive intermodulation PIM signal strength corresponding to a first cell is determined based on a preset signal strength evaluation model and the first characteristic data corresponding to each of the N cells, to accurately estimate impact of the first PIM signal on the first cell.