The perovskite lattice strain correlating to its physical chemistry not only impacts the optoelectronic properties but also the long‐term stability. The relaxation of perovskite lattice strain has been recognized as an important pathway to improve photovoltaic performance and broaden the application scope. With the growth of research interest and the thriving of synthetical approaches in strain engineering, it is particularly necessary to summarize the current strategies to give an in‐depth understanding of the relaxation of lattice strain. Herein, the milestones in strain relaxation studies are summarized and the theoretical simulation and methodological approach to correlate the crystal structure and physical properties at an atomic level is outlined. This perspective provides fundamentals to theoretically predict and experimentally measure the strain relaxation effect and suggests design principles and synthetical strategies for tackling the lattice strain issue for perovskites. The relaxation of perovskite lattice strain has been recognized as an important pathway to improve photovoltaic performance and broaden the application scope. This perspective provides fundamentals to theoretically predict and experimentally measure the strain relaxation effect and suggests design principles and synthetical strategies for tackling the lattice strain issue for perovskites.