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Background The content of medicinal bioactive constituents in huangqi is affected by plant age. In this study, we devised a quick and convenient method for determining the age of huangqi, which was cultivated in Hunyuan County (Shanxi Province). Methods 1, 2, 3, 4, 5, 8, 10 growth years huangqi had 38 samples, all samples were collected separately. The growth rings in these samples were observed after making paraffin section and freehand-section. The relationship between growth rings and its growth years was analyzed by SPSS 19.0 software. Histochemical localization of total flavones and saponins in huangqi was determined by color reactions. The concentration of four flavonoids and two saponins in the roots of huangqi of different ages and different organizational structure (normal roots and rotten heart roots) were determined by HPLC-DAD and HPLC-ELSD. The results were analyzed by SPSS 19.0 software. Results All huangqi samples had clear growth rings, and the statistical result about growth rings (X) and growth years (Y) showed significant correlation (r = 1, P = 0.000). The calibration curves of these six ingredients showed good linearity respectively, with significant correlation. All relative standard deviations (RSDs) of precision, recovery, repeatability, and stability experiments were less than 2%. Roots of 5-year-old plants contained the highest concentrations of total flavonoids and saponins. Saponin concentrations increased toward the center of the roots, whereas the four flavonoids showed an opposite trend in tissue distribution. Conclusion The growth year of huangqi (Hunyuan County, Shanxi Province) could be determined soon and conveniently by naked eyes after staining phloroglucinol-HCl solution on freehand section. The content of saponins and flavonoids in rotten heart root and the surrounding normal tissues were affected by the formation and the extent of rotten heart. Electronic supplementary material The online version of this article (doi:10.1186/s13020-017-0135-z) contains supplementary material, which is available to authorized users.