The time resolved fluorescence spectra and steady state spectra of four kinds of APCs have been studied. The data have been analyzed in terms of a sum of exponensials by Monte Carlo method. The results show that two bands appear in API and APB fluorescence spectra at 662 nm and 680 nm with different lifetimes (662 nm APC I: 35.8 ps, 1.67 ns; APB: 36.6 ps, 1.45 ns; 680 nm APC Ⅰ: 34.2 ps, 1.64 ns, and APB: 25.8 ps, 1.62 ns); while for APC Ⅱ and APC Ⅲ, only one peak exists at 660 nm with different lifetimes (APCⅡ:20.4 ps, 1.64 ns; APCⅢ :23.8 ps,1.76 ns). The results indicate that there are two paths of energy transfer in core of PBS and imply the ultrafast energy transfer processes of the APCI and APCB trimers.