The invention relates to an in-situ warm-mixing regenerant for a bituminous pavement, and a preparation method and a construction method of the in-situ warm-mixing regenerant. The strength of a cold-regenerating mixture is longer in formation time; a finish coat in a certain thickness is required to be paved additionally; the property of the regenerated mixture is poorer; a lower level cold mixing technology is used generally; and cement is required to be added generally, so that the durability of the level is reduced. The in-situ warm-mixing regenerant for the bituminous pavement comprises the following raw materials in parts by mass: 10-30 parts of naphthenic hydrocarbon, 20-40 parts of furfural extract oil, 30-50 parts of deionized water, 10-20 parts of microwave absorption agent, 5-10 parts of surfactant, 5-10 parts of dispersing agent and 1-5 parts of antiaging agent. According to the in-situ warm-mixing regenerant, the preparation method and the construction method, the mixing cost can be lowered; the construction efficiency is improved; a use ratio of old materials is increased; compared with in-situ heat regeneration, the ageing of a bituminous mixture is reduced; the service life of the pavement is prolonged; a cooling rate is reduced; the discharge amount of harmful gas and dust is decreased; new aggregates and new bitumen are not required to be added; and the material cost is lowered.