Abstract: To reduce the cost of the small-sized data acquisition system, has developed a data acquisition system of hydrostatic testing machine for welded steel pipe by means of fully using the S7-200 built-in PPI Protocol. Described here in the article are the main aspects of the said protocol, including the format, communication process and examples of read write command and application, etc. The operation practice shows that the newly-developed data acquisition system is not only cost-effective and easy to operate, but also capable of providing consistent and reliable data acquisition.