Abstract: In order to solve the problem of nitrate contamination in groundwater, dynamic simulation column studies on compost and compost+iron chip promoting in-situ bio-remediation were carried out. The objectives were to investigate the operating performances, to explore the changes in hydrochemical parameters, to analyze the transformation processes of nitrate, to identify the effects of groundwater velocity and influent nitrate concentration, to broaden the types of fiber-based solid organic carbon sources and to improve their denitrification rates. Results show that NO₃^- removal efficiencies of compost and compost+iron chip were 75.08%-79.57% and 82.24%-86.48%, respectively. Using compost for in-situ biological denitrification is feasible and efficient, and compost+iron chip performs better for nitrate removal via hydrogenotrophic denitrification. At the beginning of operation (≤ 8 d), compost readily led to the effluent NO₂^- concentration above the Chinese drinking water standard (GB 5749-2006), and meanwhile compost+iron chip readily resulted in the effluent NH₄⁺ concentration above the Chinese drinking water standard (GB 5749-2006). Denitrification rates of compost and compost+iron chip were 9.69 and 11.30 g·m^-3·d^-1, respectively, which were significantly higher than the value of saw dust (0.30 g·m^-3·d^-1). Total organic carbon (TOC) increment (≤ 18.34 mg·L^-1) was kept stable during the period of 25-100 d for compost. During the period of 0-100 d for operation, effluent pH was always lower than the corresponding influent value for compost. The similar trends of TOC and pH were observed for compost+iron chip. After 10 d, most of the influent NO₃^--N was transformed into gaseous nitrogen in the presence of compost and compost+iron chip, respectively. Removal efficiency decreased from 76.84% to 48.32% for compost and from 85.22% to 55.98% for compost+iron chip with Darcy velocity increasing from 0.5 to 2.0 m·d^-1. Removal efficiency decreased from 76.44% to 44.87% for compost and from 85.42% to 65.46% for compost+iron chip with influent NO₃^- concentration increasing from 100.58 to 301.02 mg·L^-1. Darcy velocity and influent nitrate concentration both have significant effects in biological denitrification performance of compost and compost+iron chip, respectively.