The ultralow emittance storage ring light source based on multi-bend achromats is an important development direction of the new generation of synchrotron radiation light source. As the first fourth generation synchrotron radiation light source in China, High Energy Photon Source (HEPS) is under construction. The physics and engineering design has been finished for HEPS. The beam energy is 6 GeV, the beam current is 200 mA, and the horizontal natural emittance is less than 60 pm∙rad, promising radiation brightness of up to 1×10²²phs·s^-1·mm^-2·mrad^-2·(0.1%bw)^-1 at typical hard X-ray regime. HEPS will be an important platform to support original and innovative research in the fields of basic science and engineering science. This paper will introduce the overall and physics design of the HEPS project.