This paper analyzes the estimation method of piping material quantity of overseas megaton ethylene plant in the quotation stage. Based on the data analysis of the piping material take-off of 7 megaton ethylene plants completed, the empirical benchmark quantity of various piping materials in different process units and the empirical ratio of some small-size materials to large-size materials are calculated, which provides a data reference for the estimation of piping material quantity in the quotation of new megaton ethylene plants.