New technique has been used to extract of lignin by adding carboxylic acid derivates and organic solvent to precipitate and extract lignin from black liquor (pulp wastewater). Through this new treatment process, new carboxylate which is decomposed to carbondioxide, water and metal oxide at the high temperature was formed. The process of using organic carboxylic acid and organic solvent to precipitate and extract lignin is low-cost and can not cause second pollution. The lignin obtained through this new process is water insoluble and thermoplastic. Its weigh average molecular weight, purity, and glass transition temperature are higher than 2000, 90% and 150°C, respectively. Through the methods of thermoplastic modification, the thermoplastic properties for high purity lignin-based composite materials are improved significantly. Its melt flow ratio, tensile strength and elongation at break are 0.73 g/10 min, 11.8 MPa, and 21%, respectively. Thermoplastic lignin-based composite materials have good processing properties as well as synthetic polymers for extruding, injection molding, and blowing processes. Lignin, as a kind of natural thermoplastic polymers with good processing properties, can be carried out to process for film, foam, and thermoplastic composite.