Abstract: Objective To value fluorescent quantified PCR (polymerase chain reaction) technique to detect the DNA of Mycobacterium tuberculosis from clinical patients.Methods Detect the DNA of TB from the sputum of 80 active tuberculosis and hydrothorax of 40 tuberculous pleuritis.At equal pace,make a comparison to proceed microscopic examination and cultivation.Results With fluorescent quantified PCR,56.2% (45/80),27.5% (11/40)positive detection from active tuberculosis and tuberculous pleuritis respectively.16.2% ( 13/80 ),0.0% positive specimen were detected with microscopic examination in two group of patients.Cultivation got 37.5% (30/80),2.5%(1/40) positive detection respectively.Conclusion Fluorescent quantified PCR was more sensitive and specific than traditional methods,and valuable in the microscopic examination and cultivation negative patients especially.