To investigate the function of rigidity tendency on discrimination learning of mentally retarded children, and to survey the effect of original training on shifted learning, a single group experiment was designed. Twenty-four mildly retarded children, equal in both sex with mean CA of 141.9 months, mean MA of 103.8 months, and mean IQ of 68, participated in this experiment. Two sets of two-choice "color-form object" were used and presented by way of a discrimination apparatus devised by the experimenter. The subjects were divided into three groups, the High, the Middle and the Low, according to their performance on original learning. Each subject´s percentage of stimulus-perseveration, number of position preference and the difference between pre-and-post performance were then calculated for the pun-pose of statistical analysis. The results of the study showed that: (1)the stronger the rigidity tendency, the poorer the discrimination work; (2)it became easier to learn intradimensional-shifted work after finishing original learning. Hence, two hypotheses of the study were proved.