ObjectiveTo explore the main mechanism of self-precipitation formed during the decoction of Sinitang（SNT）， and to provide a research basis for exploring the differences in the toxic and effective components of this compound. MethodsThe average precipitation yields of SNT， Glycyrrhizae Radix et Rhizoma（GRR）-Aconiti Lateralis Radix Praeparata（ALRP） decoction（GF）， ALRP-Zingiberis Rhizoma（ZR） decoction（FJ）， GRR-ZR decoction（GJD）， ALRP decoction（FZ）， ZR decoction（GJ） and GRR decoction（GC） were determined. The four main self-precipitation samples of SNT， GF， FZ and GC were physically characterized by particle size， scanning electron microscopy（SEM）， pH， total dissolved solids（TDS）， conductivity， and Fourier transform infrared spectroscopy（FT-IR） analysis. The chemical compositions of SNT decoction and its different phases was identified by ultra-performance liquid chromatography-quadrupole-electrostatic field orbitrap high-resolution mass spectrometry（UPLC-Q-Exactive Orbitrap-MS） for SNT， SNT self-precipitation and SNT supernatant， and the contents of its main toxic and effective components were determined by high performance liquid chromatography（HPLC）. ResultsPrecipitation yield results of the 7 samples of SNT decoction and single decoction showed that SNT had the highest self-precipitation yield. The formation of SNT self-precipitation was mainly related to the reaction between ALRP and GRR components to form complexes， and FT-IR showed that GRR had the greatest influence on the formation of self-precipitation. A total of 110 components were identified in the SNT decoction， including 100 components in the SNT self-precipitation and 106 components in the SNT supernatant. And quantitative results of the main toxic and effective components revealed that the reaction between ALRP and GRR components formed complexes， resulting in the following content hierarchy for free components：SNT decoctionsupernatantself-precipitation， these components included free liquiritin， benzoylmesaconine， benzoylaconitine， benzoylhypacoitine， liquiritigenin， aconitine， hypoaconitine， isoliquiritigenin and ammonium glycyrrhizinate. ConclusionSNT exhibits spontaneous precipitation during compound decoction， with GRR exerting the greatest influence on its formation. This suggests GRR plays a significant role in the detoxification of SNT. The differences in the self-precipitated toxic-effective components of SNT compound decoction primarily manifest as changes in component content， reflecting the characteristics of SNT "deposition in vitro and sustained release in vivo" and the importance of "administered at draught" in the clinical application of SNT.