Unlike ferromagnets, which can only support the GHz range, THz dynamics in antiferromagnets (AFM) is generally excited by femtosecond pulsed laser. However, the nature of the fundamental mechanism of spin dynamics with optical excitation in 2D antiferromagnets is not yet fully understood. As a representative of 2D AFM semiconductors, the experimentally exfoliated MnPS3 monolayer exhibits several advantages for spintronic applications. A team led by Prof. Jijun Zhao from the School of Physics, Dalian University of Technology, China, investigated the competition between electron-phonon-coupling (EPC) and spin-orbit-coupling (SOC) during the photoexcited spin dynamics process of AFM MnPS3 monolayer based on ab initio nonadiabatic molecular dynamics (NAMD). The optically induced mid-gap states of the S-p orbitals not only facilitate electron hopping by lowering the excitation energy, but also enhance the SOC effect between S-p and Mn-d orbitals. As a result, the phase transition from the AFM to the ferromagnetic state can be realized at an experimentally achievable electron-hole pair density of 1.11 1014 cm-2. The excited electrons first relax to the mid-gap states without spin flip through EPC, and then to the d orbitals in opposite spin states via SOC, which effectively prolongs the photogenerated carrier lifetime to 648 fs. The optically driven magnetic phase transition makes AFM MnPS3 monolayer a favorable candidate for information storage.