According to the present invention, there is provided a method for preparing low molecular weight amorphous polypropylene. In contrast to the prior art in which amorphous polypropylene is prepared by injecting an internal donor and an external donor upon preparing a primary catalyst, the present invention enables easier preparation of low molecular weight amorphous polypropylene and a copolymer thereof by simply mixing a primary catalyst with an alkylaluminum-based co-catalyst without injecting an internal donor, upon preparing a primary catalyst, and an external donor, upon polymerization. According to the present invention, the primary catalyst has superior reactivity with hydrogen, as chain transfer agent, allowing for preparation of low molecular weight amorphous polypropylene even under low hydrogen pressures and low-pressure driving conditions.

According to the present invention, there is provided a method for preparing low molecular weight amorphous polypropylene. In contrast to the prior art in which amorphous polypropylene is prepared by injecting an internal donor and an external donor upon preparing a primary catalyst, the present invention enables easier preparation of low molecular weight amorphous polypropylene and a copolymer thereof by simply mixing a primary catalyst with an alkylaluminum-based co-catalyst without injecting an internal donor, upon preparing a primary catalyst, and an external donor, upon polymerization. According to the present invention, the primary catalyst has superior reactivity with hydrogen, as chain transfer agent, allowing for preparation of low molecular weight amorphous polypropylene even under low hydrogen pressures and low-pressure driving conditions.