The characterization and noise mitigation of laser interferometer gravitational-wave detectors constitute a cornerstone in the advancement of gravitational-wave astronomy. Ground-based laser interferometers such as LIGO, Virgo, and KAGRA have established comprehensive detector characterization frameworks that integrate physical environmental monitoring, data-quality vetoes, and event validation procedures, enabling the confident detection of hundreds of gravitational-wave events. This review provides a systematic overview of the principles, methodologies, and practical techniques of detector characterization, with a focus on their application to both ground-based and space-based detectors. For ground-based interferometers, we describe the architecture and functionality of the Physical Environmental Monitor (PEM) system, which plays a crucial role in identifying coupling pathways between environmental disturbances and the interferometer strain channel. By combining multi-channel sensor data with statistical correlation analyses, the PEM system enables quantitative assessment of noise sources and supports targeted mitigation strategies. We further review a range of widely used online and offline algorithms, including time–frequency analysis tools and hierarchical veto methods, highlighting their roles in glitch identification, classification, and spectral characterization. In addition, key noise suppression techniques are summarized, such as Wiener filtering for subtracting linearly coupled noise, as well as gating and inpainting methods for mitigating transient noise artifacts. For space-based missions, particular emphasis is placed on the LISA Pathfinder mission, which serves as a critical technological demonstrator for the future Laser Interferometer Space Antenna (LISA). Experimental results show that LISA Pathfinder have exceeded its design requirements, achieving residual acceleration noise levels compatible with LISA sensitivity goals. Detailed in-orbit analyses have identified dominant noise contributions, including actuation noise, Brownian noise, and stray electrostatic effects, as well as transient disturbances (glitches) whose physical origins remain partially unresolved. These findings provide valuable insights into the low-frequency noise environment and the challenges of operating precision interferometry in space. Based on the observational results from LISA Pathfinder and the extensive experience accumulated in ground-based detector characterization, this review presents key recommendations for future space-based gravitational-wave detectors from multiple perspectives, including data analysis, detector design, engineering implementation, and end-to-end data processing. These include the development of comprehensive multi-channel monitoring systems, the integration of data-driven and physics-based modeling approaches, and the refinement of methods for non-stationary and non-Gaussian noise. Particular attention is given to challenges associated with intersatellite laser link alignment, pointing stability, and clock synchronization, as well as the resulting noise coupling mechanisms. Furthermore, the impact of multi-spacecraft configurations on the transferability of existing characterization algorithms is discussed, highlighting limitations arising from distributed sensing, time-delay interferometry, and the increased dimensionality of auxiliary channels. Overall, these advances validate the feasibility of gravitational-wave detection in the sub-millihertz regime and provide essential guidance for upcoming missions such as LISA, Taiji, and TianQin.