The invention discloses a realization method for traditional group calling triangular positioning of a digital cluster communication system in the light of the problem that the triangular positioningbusiness cannot obtain correct EPN under the condition that the preceding reversion channel of the existing PTT traditional group cluster system is shared. The invention comprises the following steps:(1) a base station receives PTT traditional group calling business message from a terminal and the bottom of the base station reports a PN and a EPN of the terminal collected by a chip to the upper application of the base station; (2) the upper application of the base station calculates target unidirectional relay or service unidirectional relay of the terminal according to the PN and the EPN andreports to a network lateral positioning center to calculate the position of the terminal. The invention dissolves the problems that correct EPN cannot be obtained when the preceding reversion channel of traditional group calling digital cluster system is shared, realizes accurate positioning of the mobile terminal, and is applicable for the existing cluster system.