Since its inception, the definition methods of the International System of Units (SI) have not remained static. With the continuous advancement of science and technology, the definitional benchmarks for SI physical quantities have gradually shifted from material artifacts to quantum physical constants. Against this backdrop, at the 26th General Conference on Weights and Measures Held on November 16, 2018, the measurement methods for all seven base units of the SI were redefined, and these new definitions officially came into effect on May 20, 2019. Consequently, SI physical quantities are now defined in terms of quantum constants rather than material artifacts, endowing the SI with greater stability and universality. This transformation represents one of the most significant changes since the creation of the SI, marking a milestone in its history and having profound implications for scientific research and industrial processes. As a result, the realization of SI base units based on the new quantum definitions has become a focal point of scientific research worldwide. This paper introduces the new definitions of the seven SI base units and explores the current international approaches to their realization based on photonic quantum principles.In this paper, both introductions on the importance of SI, and new definition methods, especially current light quantum methods, of basic units in SI have been implemented. Then, development of SI has been prospected, for providing research ideas and a way to rapidly understand relative contents for researchers. Based on investigations on abundant domestic and abroad literatures and works, combined with study experiences from authors of this paper, new definition method for seven basic units in SI has been described in detail. Then, the latest domestic and abroad realization method for obtaining basic unit values in SI has been analyzed and concluded.In recent years, the rapid development of quantum optical measurement methods has led to breakthroughs in various detection technologies, including but not limited to single-photon detectors, single-photon sources, photon-number-resolving detectors, and photon detection surpassing the standard quantum limit. While these advancements have promoted the development of quantum metrology standards related to optical radiation, they have also introduced new challenges in single-photon metrology. In the field of candela quantization research, the United States has been a global pioneer in comprehensively advancing key technologies for photon metrology standards, achieving significant milestones such as high-speed superconducting nanowire single-photon detectors with detection efficiencies exceeding 90% and pW-level absolute cryogenic radiometers monitored by superconducting transition-edge sensors. Since 2008, the European Union has initiated research programs under the banner of the "Quantum Candela", establishing a roadmap framework for developing optical radiation standards based on photonic quantum principles.The current SI base units are established by linking the units to defining constants through modern quantum science and technology, representing an innovative approach in the evolution of the SI and a significant milestone in its scientific and technological progress. In the future, any newly discovered physical phenomenon that can establish a clear relationship between a physical quantity and an SI defining constant can be utilized to realize SI units. With the advent of the quantum era of the SI, quantum technology-based metrological standards, particularly those based on photonic quantum standards, are being increasingly refined and matured, continuously pushing the boundaries of precision. A new quantum-based international measurement system will consequently be redefined. Furthermore, the new definitions of SI base units are driving the development of next-generation quantum measurement instruments, enabling more accurate and reliable measurements, shortening and flattening the traceability chain, and significantly impacting and challenging national governance systems, management frameworks, and traditional human perspectives.