The heavy metal contaminants in soil can damage soil productivity and consequently made the agricultural production suffered heavy losses. In China, it’s a common sense that the vegetable field is suffering Cd enrichment. Lettuce, a widely consumed vegetable, is very sensitive to the presence of toxic elements in soil, and these elements can accumulate in the edible parts of the plant and do harm to human body thorough the food chain. So it’s very important to know how the lettuce response when the soil was polluted by Cd. In our early study we found that Cd uptake in lettuce differed significantly among several lettuce cultivars after planted in a same Cd-contaminated field. We thought this difference may due to the different reactions of lettuce root exudation to cadmium stress, and to test it a hydroponic culture experiment was implemented. In this study, four lettuce varieties (‘American fast growing lettuce’, ‘Daxiangsheng No.2’, ‘FashiCai Huaye Kuju’ and ‘Lisheng No.2’) were cultivated in 10 mg·L^-1 Cd contained Hoagland solution for three weeks. The water culture method was used to obtain the root secretion solution at the end of every week. The TOC content (mg·L^-1·h^-1) of the root secretion solution was used to characterize lettuce roots secretion capacity, the 3D fluorescence spectrum scan results of the root secretion solution was used to characterize types of lettuce roots secretion, the soil extracted cadmium concentration by the root secretion solution was used to characterize the capacity of lettuce roots secretion to activate soil cadmium. The results showed that the roots secretion capacity was increased by incubation time, while the number of root secretion and cadmium activation capacity of root secretion showed a trend of decrease. The root secretion capacity was both significant negative related to the root secretion activate ability to soil cadmium (r= 0.78，P <0.01)， and types of root secretion (r=0.59，P<0.01), while the root secretion activate ability to soil cadmium was significant positive related to the types of root secretion (r=0.69，P<0.01). That meant while under cadmium stress, the lettuce roots secretion capacity would increase while the types of root secretion would decrease, that would result in the reducing of Cd activation ability of the lettuce root secretion.