ATRP has been recognized as a powerful tool to synthesize polymers with well-defined structures, narrow polydispersity, and controlled molecular weight in the past decades. Usually, it is believed that the typical side reactions (such as termination and chain transfer reactions) in typical radical polymerizations could be inhibited in ATRP for the persistent radical effect. More recently, some researchers did notice that some chain transfer reaction to N containing ligands happens in ATRP. However, the chain transfer constant (k(tr)/k(p)) in ATRP has never been able to be measured experimentally due to the difficulty of determining the precise composition of the resultant polymer. Therefore, the influence of chain transfer reaction onto ATRP has rarely been discussed. In this work, we provide a novel method to determine the competition between chain transfer reaction and initiation reaction of free radicals (k(tr)/k(i)) by analyzing the structure of grafting copolymers from poly(vinylidene fluoride-co-trichlorofluoride ethylene) P(VDF-co-CTFE). The perfect coincidence of experimental results with theoretical ones indicates that the method may help to understand the chain transfer reaction in ATRP as well as its influence on the chain end of resultant polymer.