In this work, a simple model is developed to explore the electron thermionic emis- sion from a single-layer graphene. This study is based on our prior efforts in showing that electron emission mechanisms from single-layer graphene is quite different from the traditional models, such as graphene field emission, and graphene laser-induced over-barrier emission, etc.. Now, we establish a new scaling for thermionic emission from graphene, quite different from the conven- tional Richardson’s law responsible for bulk materials. Our analytical formula obtained in this work is demonstrated to agree well with numerical results.