In this work, the long-chain branched polylactide (LCB-PLA) with free gel is prepared by the introduction of cyclic organic peroxide (COP) into linear PLA (L-PLA) through reactive extrusion. Due to the formation of LCB structures, the melt strength and crystalline properties of PLA are significantly improved, leading to obviously enhanced foaming property and heat resistance. Specifically, with the addition of 0.5 wt % COP, the strain hardening coefficient (X-E) is sharply increased to about 4.8, the nucleation efficiency reaches 74.5%, and the crystallinity is raised by 15 times. Correspondingly, the expansion ratio of the foamed LCB-PLA reaches 50-fold, and the Vicat softening temperature is increased from 60 degrees C to above 150 degrees C after simple annealing treatment. Thus, this study provides a simple and effective strategy to simultaneously improve the foaming performance and heat resistance of PLA, which is of great significance for the PLA industrialization.