Solar Energetic Particles (SEPs) are composed of protons, electrons, and heavy ions with energies ranging from hundreds of keV to MeV. They are accelerated in magnetic reconnection regions (impulsive events) and by Coronal Mass Ejection (CME)-driven shocks (gradual events). Large-scale SEP events are one of the most important phenomena in terms of space weather. They pose a risk of radiation exposure to humans and equipment in space. In this presentation, I will show the study of the large SEP sources using extreme-ultraviolet (EUV) images and Potential Field Source Surface (PFSS) extrapolations from the conventional magnetograms and AI-HMI magnetogram on a near real-time basis. The features of SEPs strongly depend on physical quantities of CMEs and flares at the connecting footpoints between the sources and the spacecraft. I will present the temporal and spatial variations of SEP fluxes observed by in-situ measurements and the relations between the fluxes and the quantities of the SEP sources.