A red-emitting phosphor MgY4Si3O13:Eu3+ was synthesized by conventional solid-state reaction for the first time. Photoluminescence spectra show that the phosphor can be efficiently excited by ultraviolet and blue light and exhibit an intense emission at 615nm due to the dominant (D0F2)-D-5-F-7 electric dipole transition of Eu3+. The decay times of Eu3+ monitored at the different wavelengths present an interesting change trend. According to the results of XRD Rietveld refinement, in a unit cell, the number of Eu3+ is obtained to be 0.064 for 4f site and 0.294 for 6h site. The remarkable preference occupancy for one site could be the leading reason of the abnormal change in decay times. The testing of thermal quenching indicates that the photoluminescence intensity of the phosphor is very sensitive to temperature and furthermore, the emission intensities from (D1FJ)-D-5-F-7 and (D0FJ)-D-5-F-7 show the different decay ratios with the increase in temperature. Based on the configurational coordinate diagram, an underlying mechanism is proposed and can explain the phenomenon reasonably. The mechanism could be helpful for the understanding of the energy transfer phenomenon among the various energy levels in the process of temperature change as reference.