Orychophragmus violaceus is an ornamental plant, whose plantlets are recalcitrant to in vitro rooting. The effect of plant growth regulators on root formation and growth rate of in vitro-growing Orychophragmus violaceus plantlets was studied. Ten treatments with different concentrations of IBA, NAA and GA₃ supplemented to half strength MS medium were carried out. The root growth rates during the logarithm growth period were obtained through measuring the root length of in vitro-growing plantlet in sterilized condition at different times. The lengths of roots in the same condition were acquired by analyzing the image from the plantlets. There was a significant correlation between the root lengths obtained from the image analysis and those from the manual measurement (Y = 1.058X + 0.027, R² = 0.993, n = 22, p ≤ 0.01). The effect of plant growth regulators combination on the formation and growth of roots was different. The earliest occurrence of roots and the optimal effect on root growth resulted on half strength MS medium supplemented with 0.05 mg l^-1 NAA, 0.5 mg l^-1 IBA and 0.003 mg l^-1 GA₃. The plant growth regulators combination of 0.5 mg l^-1 NAA, 5 (or 0.05) mg l^-1 IBA and 0.01 mg l^-1 GA₃ was disadvantageous for the formation and growth of roots. Whereas, the plant growth regulators combination of 0.05 (or 0.0015) mg l^-1 NAA, 0.5 mg l^-1 IBA and 0.1 mg l^-1 GA₃ was advantageous for the formation and growth of roots.