Base on the angular spectrum theory and sampling theorem, recording condition and the size of suitable object are discussed during an in-line hologram recorded in given sampling frequency. The total size of CCD, detecting unit size and pitch limit the size of object and recording distance. Under the condition that sampling condition is satisfied, recorded hologram could contain three-dimensional information about object. Starting with this principle, application range is presented when a CCD with given parameters is used to record a hologram.