A simple, rapid, and sensitive ultra-high performance liquid chromatography with charged aerosol detector (UPLC-CAD) method was developed for firstly simultaneous determination of seven oligosaccharides, including two pairs of linear oligosaccharides isomers (DP3-1, DP3-2 and DP4-1, DP4-2) and 3 high branched oligosaccharides (DP 5, 6 and 7), as well as sucrose in Pseudostellaria heterophylla. The separation was performed on a Waters BEH Amide column (2.1 × 150 mm i.d., 1.7 μm) with gradient elution within 20 min. All calibration curves for the investigated analytes showed good linearity (R > 0.9992). Their limits of detection (LOD) and quantification (LOQ) were in the ranges of 0.24–1.35 μg/mL and 0.78–4.96 μg/mL, respectively. Repeatability of all investigated components detected in samples was less than 2.9%. All the recoveries of each analyte ranged from 99.2% to 104.3% were acceptable. An ultra-high performance liquid chromatography–tandem quadrupole time-of-flight mass spectrometer (UPLC-QTOF MS) method was also applied to authenticate the oligosaccharides in different samples by comparing to the isolated standards. Oligosaccharides, especially linear oligosaccharides isomers and high branched oligosaccharides with different degree of polymerization (DP), were firstly identified and determined in P. heterophylla. Their contents in 33 samples of P. heterophylla from different locations was successfully compared, which is helpful to evaluate its quality.