Total organic carbon(TOC) can be determined by means of combustion and flame ionization detector. The principle of string method is that a sample acidified to pH2 and transferred into combustion tube by string is oxidized with air. Another combustion tube method is that organic compounds are oxidized in the combustion tube charged with CuO and cobalt asbestos after the acidified sample is injected directly by microsyringe. Carbon dioxide evolved was reduced under specially treated nickel catalyst and hydrogen, the methane produced was detected by flame ionization detector. Linear relationship was found between concentration and the peak height by the string method. The peak area in the case of combustion tube method is in the range of 1-200ppm. The coefficient of variation by string method was 2.3% and that by combustion tube method was 1.8%. The lower detectable limit was about 10mol. Advantages of the latter are simplicity, sensitivity and reproducibility. TOC in contineous stream can also be determined automatically by means of the string method.