The invention discloses a detecting method for the number of one-section-multi-cluster fracturing fractures in a horizontal well. The detecting method includes the follows steps that firstly, basic data of a fracturing well with the same reservoir development characteristics and the same layer as the horizontal well in a block are collected; secondly, a fracture pressure calculation model is established based on the logging data; thirdly, the fracture pressures of one-section-multi-cluster fracturing points are predicted by using the fracture pressure prediction model obtained in the second step; fourthly, the closure times and closure pressures of the fractures and fracture fluid loss characteristic information are analyzed and judged by testing pressure drop data of fracturing; fifthly,G function analysis is performed on construction data collected from the fracturing test by using PT or a Stimplan fracturing software; and sixthly, opening and extension conditions of the one-section-multi-cluster fracturing fractures are judged, design optimization of the remaining fracturing sections is conveniently guided. The detecting method for the number of one-section-multi-cluster fracturing fractures in the horizontal well has the beneficial effects that the number of the one-section-multi-cluster fracturing fractures in the horizontal well can be detected in real time and effectively, the effectiveness of one-section-multi-cluster is ensured, and the effect of horizontal well reconstruction is ensured.