Abstract: Pyrolysis can convert biomass into pyrolysis gas, coke, and bio-oil, offering significant advantages in the high-value utilization of biofuels and the production of high-value added chemicals. Recently, the use of phosphorous catalysts in biomass pyrolysis to produce chemicals such as levoglucosan, furans, and high-surface-area activated carbon has received increasing attention. However, research has mostly focused on the directed preparation of bio-oil, and the effects of solid phosphoric acid on biomass catalytic pyrolysis are not well understood. To explore the catalytic performance of solid phosphoric acid in biomass pyrolysis, this study prepared a quartz sand-based solid phosphoric acid catalyst (PS) using an impregnation method and conducted catalytic pyrolysis experiments on poplar wood. A diatomaceous earth-based solid phosphoric acid catalyst (PD) was also prepared for comparison. First, the catalysts were characterized using BET, SEM, and XRD techniques. By comparing the composition and morphology of the catalysts before and after the reaction, the catalytic mechanisms during pyrolysis were hypothesized. Then, pyrolysis experiments were performed to investigate the effect of the PS catalyst and its addition ratio on the yield and composition of pyrolysis products. The results showed that PS reduced the yield of pyrolysis gas by 32.2% to 41.2% compared to non-catalytic pyrolysis, while increasing the yield of coke by 18.8% to 28.2%. This could be attributed to cross-linking reactions between the phosphoric acid and the macromolecular organic structures in the poplar wood. In terms of pyrolytic gas, the proportion of CO increased by 27.1% to 32.4%, whereas the proportions of CH₄, CO₂, and C₂-C₃ decreased to varying extents, leading to a reduction of 5.6% to 16.2% in the heating value of the gas. Furthermore, PS significantly enhanced the selectivity of furan compounds in the bio-oil. When the PS-to-poplar wood ratio was 1:1, the relative abundance of furan compounds reached up to 88.6%. Although PD also enhanced the selectivity of furan compounds in the bio-oil, its effect was significantly lower than that of PS. In terms of char, the carbon retention rate was increased by 40.6% to 72.3% in the catalytic pyrolysis compared to non-catalytic pyrolysis. Analysis indicated that active species in PS formed C-O-P, C-PO₃, and C₂-PO₂ chemical bonds on the char surface through cross-linking reactions with the oxygen-containing functional groups of the biomass, which inhibited the cracking of side-chain structures. In contrast, PD only improved the carbon retention rate by 6.8%, indicating a much lower solid carbon retention effect compared to PS. Based on the analysis of the products from solid phosphoric acid-catalyzed pyrolysis of poplar wood, it was found that PS exhibited strong selectivity for furan compounds in bio-oil, showing potential for the production of furans from biomass pyrolysis. Additionally, PS significantly improved the carbon retention rate in char through cross-linking reactions with oxygen-containing functional groups. These results confirm that PS has significant potential in the preparation of furan chemicals and in improving the carbon retention rate during biomass pyrolysis. These findings provide valuable insights into the development of new solid phosphoric acid catalysts and the high-value utilization of lignocellulosic biomass.