Abstract In Computerized Adaptive Testing (CAT), it costs a lot to build items. When the items are over exposure, the examinees are easy to take the same items. The security and equity of the test are questions. The ability distribution based SHC（ASHC）Procedure was proposed by Sheng- Tso Chen. They fund that ASHC improve measurement precision and maintain controlling of items exposure well by comparing with SHC Procedure. However ASHC procedure have to get the ability distribution of the examinees before testing. Item exposure parameters of ASHC can be obtained only through time-consuming simulations prior to operational. Besides, ASHC’s maximum item exposure rate is too large in some conditions. The purposes of this study are to implement ASHC online with freeze procedure, and to compare ASHCOF with others online approach. The results showed that ASHCOF can improve controlling of items exposure and maintain measurement precision well by comparing with ASHC Procedure. In case of lower exposure controlling and larger item pool, ASHCOF is a better choice of the online approach.
