In recent years, the development of single-cell sequencing technology has significantly advanced our understanding of single-cell genomics and transcriptomics. However, the study of proteomics, directly related to single-cell life processes, has been limited by slow technological progress. With advancements in sample preparation techniques and chromatography-mass spectrometry instruments, the analytical sensitivity of single-cell proteomics (SCP) has markedly improved. In this review, we thoroughly examine the development of SCP and its applications in life sciences. Regarding sample preparation, various methods such as gentle acoustic dispensing, microfluidic chips, and laser microdissection have been developed for single-cell sorting, gradually transitioning from multi-step to one-step processing, thereby reducing sample loss. In mass spectrometry, both label-free quantification and methods based on isotopic and isobaric labeling have been extensively explored, each with their own technical strengths and weaknesses. SCP has unveiled new biological insights in early embryonic cell development, stem cell differentiation, and spatial heterogeneity of liver tissues. Finally, we summarize the current challenges facing SCP technology, including detection throughput, cost, and data analysis complexity, while envisioning its future directions and emphasizing its broad potential in basic research and clinical applications.