The components of the effluent from the chemical pretreatment of poplar alkaline peroxide mechanical pulp(APMP) were analyzed in this study. The main dissolved organics were low-molecular weight(LMW) lignin, oligosaccharides, and monosaccharides. The lignin and sugar concentrations in the effluent obtained using different chemical pretreatment conditions and chemical dosages were analyzed using ultraviolet(UV) spectroscopy. This analysis provided a theoretical basis for the subsequent treatment and utilization of APMP effluent. The experimental results showed that the dosages of NaOH, H₂O₂, and Na₂SiO₃ in the chemical pretreatment process affected the lignin and sugar concentrations in the effluent and that different chemicals had differing degrees of influence. The degree of influence exhibited the following order: NaOH > H₂O₂ > Na₂SiO₃. More specifically, the dosages of NaOH and H₂O₂ had stronger influences on the lignin and sugar concentrations than that of Na₂SiO₃. Indeed, the Na₂SiO₃ dosage hardly affected the lignin and sugar concentrations in the effluent, but Na₂SiO₃ could stabilize the chemical pretreatment system and improve the reactive efficiency of NaOH and H₂O₂. The pretreatment temperature and time also affected the organic components, and the influence of the temperature was stronger than that of time.