Abstract: The traditional pig tracking and positioning technologies can not be applied universally due to the restriction of pipelines and surrounding environments. The pig tracking and positioning technology based on differential pressure attracts more and more attention owing to its advantages of sensitive pressure signals and surrounding influence independence, but its positioning algorithm is less studied. In this paper, the online pig positioning algorithm based on pressure wave was proposed for the differential pressure based pig tracking and positioning technology by taking the pigging operation in Wuhan oil transfer station, Changsha Oil & Gas transportation Sub-company of PetroChina Pipeline Company as an example. The algorithm is divided into three parts. Firstly, the signals acquired during the pigging are analyzed and divided into five states, i.e., stable pressure, pig passing valve chamber, increasing pressure, decreasing pressure and struck pig. Secondly, the states of pressure signals are distinguished by means of wavelet singularity detection and correlation analysis. And thirdly, the online pig positioning algorithm is worked out for normal operation and struck state. The algorithm was verified by using the data acquired on site. It is shown that this online pig positioning algorithm can position the pigs accurately and monitor the whole process of pigging operation.