NOVELTY - Extracting caffeine comprises adding waste tea powder and clean water in a kettle, stirring to obtain mixture, heating the mixture, concentrating the mixture, decompressing the concentrate, adding calcium oxide powder and ethanol solution, extracting the mixture, then filtering, decompressing and concentrating the extracted liquid, crystallizing, cooling to obtain caffeine crude product, adding the product and clean water into a dissolution tank, heating, adding active carbon to decolor, filtering the mixture, crystallizing, centrifugal separating the crystals, and drying.    USE - The method is useful for extracting caffeine (claimed).    ADVANTAGE - The method is capable of extracting caffeine with increased efficiency in a cost-effective manner.    DETAILED DESCRIPTION - Extracting caffeine comprises adding waste tea powder in an extraction kettle, adding 2-3 times of clean water, stirring to obtain mixture, heating the mixture to boil for 2-3 hours, stop heating, reducing water temperature to 95 degrees C, passing the mixture into a concentrated kettle to obtain concentrate having liquid density of 1.26-1.30 g/ml, decompressing the concentrate, adding tea powder quantity 1/3 of calcium oxide powder in half-dry state into the concentrate, then adding 70% of ethanol solution, stirring to obtain mixture, alcohol extracting the mixture for 3-5 hours, filtering the extracted mixture to obtain alcohol extracted liquid, decompressing and concentrating the extracted liquid to obtain concentrate having liquid ethanol content of less than 1%, adding the filtered liquid into a crystallizing tank, cooling to crystallize for obtaining crude caffeine product, adding the crude product into a dissolution tank, adding 10 times of clean water, heating to boil, adding proper amount of active carbon for decoloring, filtering the mixture to obtain filtered liquid, then adding into a crystallizing tank for crystallization, centrifugal separating the crystals, drying the crystals at 60-65 degrees C.