A low density, high-strength, degradable temporary plugging agent which includes 60% by weight to 85% by weight of polylactic acid, 5% by weight to 20% by weight of a starch, 5% by weight to 10% by weight of polycaprolactone, 2% by weight to 5% by weight of a solubilizing agent, and 2% by weight to 5% by weight of a toughening agent, based on 100% by weight of the total weight of the agent. The rigid agent can result in bridge plugging in existing cracks, with a significant increase in pressure. The preparation method is simple, the process requirements are low, and industrial production can be realized. When applied to temporary plugging fracturing, under formation conditions, it can be completely degraded within a certain period of time and will not cause secondary damage to the reservoir, while preventing the agent from polluting the formation and the occurrence of pump accidents.