Abstract: Facing the demand of unified measurement units outside the earth, we propose the consistency between ground and out of the Earth around basic theory, and technology in various major of metrology, so we have carried out a systematic study on Space Metrology, The system is divided into three directions: theory, technology and management. The theory of Space Metrology is mainly based on the theory of general relativity and Data inversion methods that ensure accurate spatial values, or space-based/ground-based calibration theories. Space Metrology technology includes space specific and space standard instruments; space natural reference; sensor in-orbit calibration; digital twin data flow transmission; remote calibration; space sensing domain metrology; space standard environment calibration technology; in-orbit manufacturing processing metrology; transportation process metrology; space remote sensing calibration and other technology. Space Metrology management includes global organizations of Space Metrology; international agreement and international standardization. Space metrology differs from traditional ground-based metrology in six key aspects: distinct metrological theories; unique spatial traceability pathways; specific spatial environmental conditions; data flow technologies for re-calibration and digital twins; coordination, synchronization, and unification of remote calibration and information sensing; and a management framework for space metrology that differs from the supervision and administration mechanisms employed in ground-based metrology. As an independent discipline or major, there must be a unique, and unlike working on the ground metrology theory and knowledge system, and the necessity, objectives, professional characteristics and research scope of Space Metrology are introduced here. As a hallmark of emerging disciplines, China’s National Metrology Development Plan has established the Space Metrology Specialty, and the national metrology technical specification administration authority has set up the Space Metrology Professional Committee.