The element distributions of intermediate mass fragments (IMF) emitted over an angular region of 5 degrees-140 degrees have been measured in the reactions of 30MeV/u Ar-40+ Ni-58,Ni-64 and In-115. Within 20 degrees-80 degrees range the IMFs with Z = 3-24 were observed. The IMF production cross section changes smoothly with its charge number, and the element distribution changes continuously when the IMF charge number increases across the charge number of the projectile. There is no strong dependence of the element distribution on the charge number of the projectile in this angular region. The transition nature of the reaction mechanism in the intermediate energy region and the power law of the IMF element distribution,as well as the dependence of element distributions on the threshold of the detectors were discussed.