To investigate the ecological adaptation strategies of drought stress on root plane and stereo geometry architecture and fractal characteristics, pot experiment using three root types of alfalfa (rhizomatous rooted Medicago sativa ‘Qingshui’, tap rooted M. sativa ‘Longdong’, creeping rooted M. varia Martin. ‘Gongnong’ No.4) as the experimental materials was conducted to set up the drought treatment experiments. The results showed that the total root length, total surface area, total root volume and root average diameter of different root-type alfalfa decreased with increasing of drought concentration. The root topological indices of different root-type alfalfa were small, and the root branching patterns were herring-bone-like. The roots of different root-type alfalfa had obviously fractal characteristics, and the fractal dimension was small, while the fractal abundance and the average link length were large, which indicated that they had simple root architecture and high ability to expand living space. Smaller branching ratio and larger stepwise branching rate of different root-type alfalfa were helpful to speed resource acquisition and promote taproot growth downward. Root architecture parameters were analyzed by the principal component analysis. The parameters of total surface area, fractal abundance, total root length, total root volume, fractal dimension, and specific root length could well present the root architecture characteristics of different root-type alfalfa. Under severe stress, the total root length, total surface area, total root volume, specific root length, and specific surface area of rhizomatous rooted and creeping rooted alfalfa were higher than tap rooted alfalfa, which showed that the adaptation to drought environment of rhizomatous rooted and creeping rooted alfalfa were stronger than that of tap rooted alfalfa.