To find out the effect of cultivation methods on vegetable root, the lettuce root length, root depth and root width radius were studied in four cultivation substrates under drip and micro-sprinkler irrigation. The result indicated that root characters of lettuce cultivated in different substrates were no significantly different at 0.05 among different irrigation methods. Based on the experimental data of lettuce root, the simulation models for lettuce root length and root depth were established using the scale of effective cumulative temperatures (DD). The root depth in different layers and DD were used as the dependent variables to establish the root width radius model. The repeat test data were employed to verify the establishing models. The root mean square error and relative error between simulated and observed values were only 290cm, 0.81cm, 0.63cm and 15%, 12%, 13% for lettuce root length, root depth and root width radius under drip irrigation and micro-sprinkler irrigation.