By organizing quantitative and qualitative information from extensive historical materials, this article aims to assess the state capacity of the Northern Song from a military-fiscal perspective, especially its fiscal capability of waging wars in the eleventh century. In response to the longstanding military threats along the northern and northwestern borders with the rivalry powers, the Northern Song state created the ruzhong provisioning system, under which the government purchased grain and fodder from civilian suppliers with the state-issued vouchers for salt, tea, and other monopoly commodities. As the vouchers turned out to be redeemable at the secondary market at Kaifeng, the voucher scheme developed into a form of public debt for the government. After the war with Tangut Xi Xia broke out, the over-issuance of vouchers in the face of the dwindling reserves of commodities and cash reserves greatly escalated the wartime inflation, damaged the credibility of these financial instruments and ultimately set the limits to the potential of the Song fiscal state in the eleventh century.