  As the matching condition in Grover search algorithm is transgressed due to
inevitable errors in phase inversions, it gives a reduction in maximum
probability of success. With a given degree of maximum success, we have derive
the generalized and imroved criterion for tolerated error and corresponding
size of quantum database under the inevitable gate imperfections. The vanished
inaccurancy to this condition has also been shown. Besides, a concise formula
for evaluating minimum number of iterations is also presented in this work.
