The purpose of this study was to develop a computerized and interactive number sense dynamic assessment system (CNSDA) on number sense to investigate the characteristics of elementary students’ performance. Number sense is the ability of awareness and reasoning for the relationships among the numbers embedded in the authentic context or situation. Around 150 fifth grade students were sampled. The results show that the adaptive hint system of CNSDA could promote the students’ number sense effectively. The correlation coefficients between CNSDA posttest and the Mathematic Computerized Adaptive Ability Test (MCAT) and the Computerized Estimation Test (CET) are higher than the static pretest. For the students with weaker number sense, CNSDA is a helpful learning and assessing resource.