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Extensive residues of neonicotinoids (neonics) have been demonstrated in food and the environment by routine monitoring measurement, but little is known about the residue levels in “ready to eat” dietary samples. To obtain a more accurate picture of dietary exposure to total neonics, an ultrasensitive and effective cleanup analytical method for the quantification of neonics in dietary samples was established on the basis of cold-induced phase separation and pre-column dilution injection liquid chromatography–high-resolution mass spectrometry. A total of 10 neonics were quantified in ultratrace amounts (ng/kg) using stable isotope dilution, with calibration curves spanning 4 orders of magnitude. Satisfactory accuracy (73.5–109.2% for the recoveries) and precision (0.6–13.2% for the relative standard deviation ranges) were obtained in method validation. Moreover, tolerable absolute matrix effects (0.89–1.09) were also obtained in 12 kinds of dietary matrices with weak relative matrix effects (2.8–12.6%). The validated method was applied to the dietary samples collected from the Chinese Total Diet Study, and the results showed that 75% of the samples were contaminated with at least one neonicotinoid.