A reaction-diffusion model is built to investigate the temporal and spatial pattes of cytoplasmic Ca2+ dynamics under the effects of Ca2+-release activated Ca2+ (CRAC) channels in T cells. Simulation results show a strong dependence of the modulation mode of Ca2+ oscillation and dynamic pattes of Ca2+ wave on the influx rate through the CRAC channel (ksoc). When ksoc is small, cytoplasmic Ca2+ is modulated as a frequency-modulation (FM) signal, whereas it shows an amplitude modulation (AM) mode after ksoc passes through a critical value. The heterogeneity in spatial Ca2+ distribution is mostly arising from the influx through CRAC channels in both FM and AM modes. During each Ca2+ spike, a more sustained cytoplasmic Ca2+ gradient is maintained in the AM mode rather than in the FM mode.