The characterization and noise mitigation of laser interferometer gravitational-wave detectors are essential for gravitational-wave astronomy. Ground-based detectors such as LIGO, Virgo, and KAGRA have established detector characterization frameworks that integrate physical environmental monitoring, data-quality vetoes, and event validation, enabling reliable detection of hundreds of gravitational-wave events. This review summarizes the principles, methodologies, and techniques of detector characterization, focusing on their application to ground-based and space-based detectors. For ground-based interferometers, we describe the architecture and functionality of the Physical Environmental Monitor (PEM) system for identifying coupling pathways between environmental disturbances and the 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 review 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, including Wiener filtering for linearly coupled noise subtraction and gating and inpainting methods for transient noise mitigation. For space-based missions, particular emphasis is placed on the LISA Pathfinder mission, a technological demonstrator for the Laser Interferometer Space Antenna (LISA). Experimental results show that LISA Pathfinder exceeded its design requirements, achieving residual acceleration noise compatible with LISA sensitivity goals. Detailed in-orbit analyses 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 insights into the low-frequency noise environment and the challenges of operating precision interferometry in space. Based on LISA Pathfinder observations and the extensive experience accumulated in ground-based detector characterization, this review presents recommendations for space-based gravitational-wave detectors in data analysis, detector design, engineering implementation, and end-to-end data processing. These include 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 introduced by multi-spacecraft configurations, including inter-satellite laser link alignment, pointing stability, clock synchronization, associated noise coupling mechanisms, and the limited transferability of existing characterization algorithms caused by 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.