A rapid method based on ultrahigh-performance liquid chromatography-quadrupole/electrostatic field orbitrap high-resolution mass spectrometry (UPLC-HRMS) was developed for the screening and confirmation of 20 mycotoxins in grain products. The samples were extracted with acetonitrile containing 2% (v/v) formic acid, and the extracts were cleaned up on Captive EMR-Lipid columns. The analytes were separated on a Thermo Hypersil Gold C column (100 mm×2.1 mm, 1.9 μm), and analyzed by UPLC-HRMS. The retention time and accurate mass of the parent ion were used for fast screening in full scan mode, while the accurate masses of the fragment ions were used for confirmation in the two-stage threshold-triggered full mass scan mode. The results revealed that the 20 mycotoxins showed good linear relationships in their respective mass concentration ranges. The correlation coefficients were not less than 0.99, and the limits of quantitation (LOQs) ranged from 0.25 to 20 μg/kg. The recoveries of the 20 mycotoxins in the sample ranged from 72.9% to 117.8% with the relative standard deviations (RSDs) from 2.9% to 15.2% at three spiked levels (=6). This method has the advantages of high sensitivity and reliability, and is thus suitable for the rapid screening and confirmation of 20 mycotoxins in grain products.