Deep space exploration, serving as a pivotal avenue for uncovering the universe's mysteries and fostering sustainable development, has emerged as the foremost strategic frontier in space technology. After decades of development, this technology has been widely used in the exploration of various celestial bodies in the solar system. In February 2015, the first deep space exploration satellite targeting the Earth, the Deep Space Observatory (DSCOVR), was successfully deployed at the Sun-Earth Lagrange Point 1 (L1), providing new perspectives and data for the study of Earth system science, while also posing new challenges to traditional satellite data research. This paper comprehensively analyzes more than 100 related papers and conference summaries published on the official website of the National Aeronautics and Space Administration (NASA) since the launch of DSCOVR. From the three levels of basic research, applied research and special research, this paper comprehensively reviews the development status, advantages and future development direction of deep space earth observation. This study reveals that deep space Earth observation can integrate existing satellite-aircraftground systems, establishing a benchmark for multi-source data fusion to create globally comprehensive, highfrequency temporal, and multi-spectral datasets for an integrated Earth observation system. It provides temporally consistent, spatially continuous, and spectrally stable global observation data, showing significant potential in the study of large-scale geophysical phenomena across the atmosphere, biosphere, hydrosphere, and lithosphere. Future advancements in sensor innovation, optimized detection technologies, and diversified observation points are expected to enable all-temporal, all-directional, and all-dimensional Earth observation. This will enhance our understanding of physical, chemical, and biological systems on Earth.