Polylactic acid (PLA) is currently the largest application of synthetic biodegradable polymer materials, so it is expected to gradually partially replace petroleum-based polyolefins and more widely used in various fields. However, the relaxation characteristics and very low crystallization rate determined by the hand-structure of PLA chains result in low melt strength and unstable molding process characteristics; meanwhile, under rapid molding conditions such as extrusion and injection molding result in poor heat resistance, tensile strength and modulus of the specimens. These problems have become the bottleneck of PLA for its larger commercialization and high-performance applications. Based on the regulation of isothermal crystallization behavior of PLA and its blends, especially the rate of isothermal crystallization and crystal morphology, the progress in the regulation and its application of isothermal crystallization behavior for PLA using various modifiers, such as chain-construct, processing flow fields and post-treatment, was summarized.