Quickly and accurately detect and analyze the intermediates and impurities produced in the synthesis of Hexanitrohexaazaisowurtzitane （CL-20）， is important for controlling the purity or quality of CL-20， and ensuring its sensitivity and detonation performance. In this study， nuclear magnetic resonance （NMR） and ultra-high performance liquid chromatography-Quadrupole time-of-flight mass spectrometry （UHPLC-QTOF-MS） were used to rapidly and efficiently analyze the impurities in the typical synthesis process of CL-20. The results showed that the impurity in HBIW was 1，3-dibenzyl imidazole， the impurity in tetraacetyl dibenzyl hexazepane （TADB） was low acylated triacetyl tribenzyl hexazepane （TATB）， and the impurity in tetraacetyl hexazepane （TAIW） was incomplete TADB. The impurities in CL-20 were not fully nitrated monoacetyl pentanitrohexazazine （MPIW） and diacetyl tetranitrohexazazine （DATN）.