In order to control the length of branched chains on Polypropylene, the effects of different quantities of silver diethyldithiocarbamate (AgDEC) on melt reactions during preparing long chain branched polypropylene (LCB-PP) via free radical grafting were studied. The LCB structure was confirmed by fourier transform infrared spectroscopy (FTIR), dynamic viscoelastic measurements and thermal analysis. The results concluded that AgDEC could efficiently control degradation of PP backbone and homopolymerization of multifunctional monomer (1,6-hexanediol diacrylate (HDDA)) in the presence of dibenzoyl peroxide (BPO) during melt grafting. Meanwhile the efficiency of forming long chain branches on PP backbone could be also increased. The dithiocarbamate radicals which are formed through the reaction between AgDEC and active free radicals (carbon centered and alkoxy species) cannot attack PP backbone and are weaker initiator for HDDA. Thus the instantaneous concentration of active free radicals is decreased, and the degradation of PP backbone and the homopolymerization of the HDDA can be controlled. Moreover, the dithiocarbamate radicals could react with the PP macroradicals and the acrylic radicals reversibly, which make longer the life time of PP macroradical and increase the reaction probability between macroradicals. compared to the initial linear PP, the LCB-PPs showed lower melt flow rate, increased crystallization temperature and improvement of the melt strenght.