The invention relates to a method for detecting a photoinitiator in a printed packaging material. The detection method comprises the following steps: extracting the photoinitiator in a printed packaging material by adopting a solvent, filtering the extract to obtain a solution for detection; subjecting the solution to ultrahigh performance bonded-phase chromatography-mass spectrometry, and quantitatively calculating the photoinitiator content. According to the provided detection method, after the photoinitiator in the printed packaging material is extracted, ultrahigh performance bonded-phasechromatography-mass spectrometry (UPC2-MS/MS) is adopted to carry out analysis; the operation is convenient, the analysis time is short, and the detection method is environmentally friendly. The detection method can realize high sensitivity detection of residual photoinitiator in a printed packaging material; the accuracy of detection of trace photoinitiator is improved, and reliable data supportis provided for the research on migration rules of a photoinitiator.