We used the Jordan-Wigner transform and the invariant eigenoperator method to study the magnetic phase diagram and the magnetization curve of the spin-1/2 alternating ferrimagnetic diamond chain in an external magnetic field at finite temperature.The magnetization versus external magnetic field curve exhibits a 1/3 magnetization plateau at absolute zero and finite temperatures,and the width of the 1/3 magnetization plateau was modulated by tuning the temperature and the exchange interactions.Three critical magnetic field intensities HCB,HCE and HCs were obtained,in which the HCB and HCE correspond to the appearance and disappearance of the 1/3 magnetization plateau,respectively,and the higher HCS correspond to the appearance of fully polarized magnetization plateau of the system.The energies of elementary excita-tion (h)ωσ,k (σ =1,2,3) present the extrema of zero at the three critical magnetic fields at 0 K,i.e.,[(h)ω3,k (HCB)]min =0,[(h)ω2,k (HCE)]max =0 and[(h)ω2,k (HCS)]min =0,and the magnetic phase diagram of magnetic field versus different ex-change interactions at 0 K was established by the above relationships.According to the relationships between the system's magnetization curve at finite temperatures and the critical magnetic field intensities,the magnetic field-temperature phase diagram was drawn.It was observed that if the magnetic phase diagram shows a three-phase critical point,which is inter-sected by the ferrimagnetic phase,the ferrimagnetic plateau phase,and the Luttinger liquid phase,the disappearance of the 1/3 magnetization plateau would inevitably occur.However,the 1/3 magnetization plateau would not disappear without the three-phase critical point.The appearance of the 1/3 magnetization plateau in the low temperature region is the macroscopic manifestations of quantum effect.