The invention discloses a long glass fiber reinforced polypropylene composite material with high thermal deformation temperature, which comprises the following raw materials by weight: 100 parts of polypropylene, 30-70 parts of long glass fiber, 3-10 parts of compatilizer, 3-12 parts of mineral filler, 1-10 parts of coupling agent, 1-5 parts of silicon carbide, 1-5 parts of beta crystal form nucleating agent, 1-5 parts of magnesium salt whisker and 0-10 parts of processing auxiliary agent. The material has high thermal deformation temperature, can be used in a wide temperature scope, and has stability and performance maintenance performance. The invention also discloses a preparation method of the long glass fiber reinforced polypropylene composite material, the preparation method is realized by employing a current double screw extruder, the preparation is easy, and the preparation method is easy to operate and implement, is in favor of industrial production, and has wide application prospect.