Trichothecenes are mycotoxins generated by Fusarium species that are toxic to humans and animals and frequently contaminate cereals. Herein, we present an UHPLC-Q-Orbitrap-HRMS method using one-step pretreatment for simultaneous detection of 16 type A and B trichothecenes in maize and wheat. A calibration strategy based on natural isotopic distribution was adopted and validated to replace traditional time-consuming and laborious multipoint external calibration curves. Various conditions influencing the method were studied. The recoveries of spiked analytes at three different concentrations ranged from 74.2% to 105.3% and the inter-day relative standard deviations were 0.5–15.6%. The limits of quantitation were 4.4–108.8 μg/kg. Moreover, the current methodology was applied to the evaluation of type A and B trichothecenes present in samples from major wheat production areas in China. This study provides a facile methodology for type A and B trichothecenes analysis and presents promising applications for exposure risk assessment of trichothecenes in cereals.