Group call is a major service in TETRA (Terrestrial Trunked Radio) networks, and there are some cases where group call conflict occurs. This paper presents a method to resolve group call conflict by merging the users requesting to initiate an existing group call into the ongoing call. In addition, this paper also comes up with a method to shorten the call set-up time by setting a time delay between call clear and channel release when the same group call is initiated frequently, and by these means user experience and system performance are improved. The state machine design and process design are described in details. The experimental test result proven the effectiveness of our method.