An ethylene bis-12-hydroxystearamide grafted glycidyl citrate (EBH-g-ECA) and a preparation method thereof are provided; the EBH-g-ECA can be used as a multifunctional auxiliary agent in a polymer material, and particularly has a chain extension and a crystal nucleation effect in a polyester polymer material. A heat-resistant polylactic acid continuously-extruded foamed material containing EBH-g-ECA is further provided. The continuous foaming technology can be realized by using the heat-resistant polylactic acid foamed material, and the prepared foamed product has a high heat resistance, a uniform appearance, a low density, and complete biodegradation. A polylactic acid foamed material preparation method for a heat-resistant is provided, which is easy to be industrialized and has a great significance for realizing the large-scale replacement of petroleum-based plastic disposable foamed products such as PP and PS.