Abstract: Etomidate is a commonly used short-acting intravenous anesthetic in clinical settings across China. Since 2022, it has replaced synthetic cannabinoids to become the most prevalent psychoactive substance identified in illicit e-cigarette oil samples. With the widespread circulation of etomidate in the illicit drug market, it was officially designated as a regulated substance in 2023. Subsequently, a variety of etomidate analogues have emerged on the illicit market. Currently, etomidate analogues are the most commonly abused new psychoactive substances (NPS) in China. In this study, gas chromatography-mass spectrometry (GC-MS) and ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF MS) were used to analyze ten etomidate-type NPS, namely butomidate, iso-butomidate, sec-butomidate, tert-butomidate, ABP-700, 2,6-diCl-3F-etomidate, 4F-etomidate, TF-etomidate, 4F-metomidate, and DF-etomidate. For GC-MS analysis, 5 mg of sample was dissolved in 10 mL of acetonitrile and ultrasonically extracted for 10 min. For UPLC-QTOF MS analysis, the prepared solution (0.5 g/L) was diluted to 0.1 mg/L with 0.05% formic acid in water (V/V) and filtered through a 0.22 μm centrifugal filter. Mass spectral data were acquired in three ionization modes, namely electron ionization (EI), electrospray ionization-collision-induced dissociation (ESI-CID) and electrospray ionization-electron-activated dissociation (ESI-EAD). The fragment ion structures and fragmentation pathways were proposed for each analyte. Etomidate analogues have multiple positional isomers; therefore, this study focused on distinguishing these isomeric compounds. Although the mass spectra of these isomers showed high similarity in EI, ESI-CID and ESI-EAD modes, accurate qualitative identification was achieved by combining retention times and ion abundance ratios. Taking butomidate, iso-butomidate, sec-butomidate, and tert-butomidate as typical examples, significant differences were observed in their retention times and abundance ratios of characteristic product ions. In EI-MS spectra, the base peak, corresponding to the most intense ion signal, which is produced through C−N bond cleavage. This fragmentation event was driven by inductive i-cleavage initiated at the N-radical center, representing the most favorable fragmentation pathway for all etomidate analogues investigated. Fragmentation pathways of etomidate analogues under ESI-CID mode showed high consistency. Initially, the M+H⁺ ion underwent C−N bond cleavage with the elimination of the R₁ group, generating fragment ion A'. This process was followed by the loss of one water molecule (H₂O) from A' to produce the secondary product ion A''. Owing to substituent variations on the phenyl ring for different etomidate analogues, downstream fragmentation pathways diverged accordingly. Compared with the CID mode, the EAD mode provided more comprehensive structural information and was more effective for distinguishing isomers. The summarized mass spectral characteristics of these ten etomidate analogues presented in this study can serve as a reference for the identification and structural elucidation of newly emerging etomidate analogues.