Nitrate and hexavalent chromium (Cr(VI)) cocontamination in groundwater has become a serious challenge for environmental health. Emulsified vegetable oil in situ technology could simultaneously remediate nitrate and Cr(VI) in groundwater, but the remediation pathways and mechanisms are still unclear. In this research, the biological denitrification processes for nitrate and the reduction and biogenic mineralization processes for Cr(VI) in a cocontaminated aquifer were studied, and the remediation mechanisms were speculated. The results indicated that the addition of emulsified vegetable oil can directionally stimulate the growth of indigenous functional microorganisms and effectively remediate nitrate and Cr(VI) in groundwater. Nitrate in groundwater could be completely reduced to nitrogen gas through biological denitrification without a short circuit. And the remediation processes of Cr(VI) can be divided into two steps: 1) Cr(VI) was reduced to trivalent chromium (Cr(III)) by microbial secondary Fe(II), 2) the reduced Cr(III) was entrapped into aquifer medium in residuals speciation through biogenic mineralization.