Abstract: The main methods for measuring black carbon mass concentration were optical absorption technique，thermal technique and thermal-optical technique． Based on the collation of the carbon data at the monitoring site in Nanmen of Suzhou City，the study compared three methods to analyze the differences． The main source differences among the three methods were as follows: the attenuation coefficient of Aethalometer had no universal standard，separation of OC carbonization and EC of the thermal technique was incomplete，and controversial temperature setting of the protocol of TOT was the main reason of the differences among the three methods．