In this paper, we present the empirical investigation results on the urban public traffic networks (PTNs). We study four urban public traffic networks in south China, which are the urban public traffic networks of Guangzhou, Changsha, Zhuhai and Xiamin. The empirical results on the four big cities show that the accumulative act degree distributions of PTNs take neither power function forms, nor exponential function forms, but they are described by two power piecewise function. We also study the accumulative act size distributions of PTNs of the four cities, and they are described with a shifted Poisson distribution. In the end we shall explain the reason why the degree distribution of PTNs is difference from that of the other complex networks.