This study investigated the role of K and steam in upgrading syngas quality over biochar in a two-stage fixed-bed reactor. The integration of K-char catalyst and steam greatly increased syngas (H2+CO) and H2 production. The syngas products yield (19.76 mmol/gbiomass) and a H2 yield (11.14 mmol/gbiomass) were achieved when K-char was used as catalyst in the presence of steam. In general, four ways could be concluded to promote volatiles reforming to improve syngas quality by K and steam: Firstly, K and steam interaction with biochar increased the surface area and developed the porous structure of biochar, providing the pyrolytic intermediates with full complete contact with the char surface, and improving the chance of contact with the active sites. Secondly, the condensation reactions of biochar were inhibited by K and steam, thus preventing the reduction of active groups on the aromatic ring of biochar. Thirdly, K and steam promoted the formation of O-containing groups with high reactive activity on the char surface, such as -COO and -CO. Moreover, volatile K migrated in biochar matrix during catalytic reforming, and steam inhibited the release of K in biochar, resulting in more K retaining on the char surface in the form of-COK and-COOK acting as the active sites, which ultimately improved the catalytic activity of biochar, and promoted tar destruction and hydrocarbon reforming.