This research aimed at establish a Computerized Adaptive Test(CAT) and remedial instruction based on the structure of competence indicators, using the “ Rational Number ” of Mathematics in Grade 4 as an example. After taking the test, students were diagnosed and given the remedial instruction effectively according to their achievement in competence indicators and the concept nodes of knowledge structure. The items of this research were based on the knowledge structure established through the experts’ and teachers’ analysis of the competence indicators. After the CAT, students could conduct the remedial instruction on their own weaknesses of the competence indicators.