A qualitative analysis method for methyl ethyl ketone peroxide (MEKP) was established by the high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) and ultra-high performance liquid chromatography-tandem quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS). The analysis method confirmed that MEKP contains six polymer forms with Eclipse plus C18 (3.0 mm×50 mm×1.8 μm) chromatographic column. To establish a data library for qualitative analysis of MEKP, the polymers of MEKP were analyzed by UPLC-Q-TOF/MS, and the fragmentation ions were collected by using the full MS/Target MS/MS modes. The six polymers of MEKP were detected in the multiple reaction monitoring (MRM) mode of UPLC-MS/MS, and the retention times and characteristic ions of these six polymers were obtained by optimizing the conditions for qualitative analysis. In the screening and analysis of the MEKP standard substance, six types of polymers were identified. High-resolution mass spectrometry and triple quadrupole mass spectrometry in MRM mode were used for qualitative analysis of polymer ion pairs, respectively. This method is sensitive and accurate for the analysis of MEKP in forensic identification.