选择性催化还原（SCR）技术是控制柴油机氮氧化物（NO_x）排放的主流技术，尿素水溶液（UWS）作为还原剂前体物在其中扮演关键角色。然而，UWS在低温、变工况下不完全分解导致的固体沉积物问题，严重影响SCR系统效率、可靠性与耐久性。本研究梳理了近年来围绕该问题的研究进展，系统总结了尿素沉积物的复杂组分构成，剖析了以异氰酸为关键中间体、以液膜为“微反应器”的详细反应机理。重点分析了排气温度、喷射参数和结构设计等多因素对沉积物生成的耦合影响规律，并在此基础之上，全面梳理了多层次的协同抑制策略，包括优化喷雾混合与热管理的物理过程调控、添加表面活性剂以改变液滴界面性质的化学改性、发展智能预测控制等。结果表明，沉积物问题的根治需基于精准的机理认知，通过系统层面的协同设计与过程融合，方可实现SCR系统在全工况、全生命周期内高效、稳定、低维护成本的运行。

Selective catalytic reduction(SCR) technology is the mainstream approach for controlling nitrogen oxide(NO_x) emissions from diesel engines, and urea-water solution(UWS) serves as the key precursor for the reductant. However, the formation of solid deposits due to incomplete decomposition of UWS under low-temperature and transient operating conditions severely impacts the efficiency, reliability, and durability of SCR systems. Recent research progress on the issue was reviewed, the complex composition of urea deposits was systematically summarized and the detailed reaction mechanism was analyzed with isocyanic acid serving as the key intermediate and the liquid film acting as a "micro-reactor". The coupled influence of multiple factors(such as exhaust temperature, injection parameters, and structural design) on deposit formation was emphatically analyzed. Multi-level synergistic mitigation strategies were further comprehensively outlined, including physical process control through optimized spray mixing and thermal management, chemical modification by adding surfactants to alter droplet interfacial properties, and the development of intelligent predictive control. The results indicate that a fundamental solution to the deposit problem requires precise mechanistic understanding, synergistic system-level design and process integration to achieve efficient, stable, and low-maintenance operation of SCR systems across all operating conditions and throughout the lifecycle.