Based on the theoretical analysis of erosion behavior impacted by flying-ash in power plant boilers,a mathmetical model of erosive characteristic for the staggered tubes is set up.A formula of relationship between the relative mass erosion rate and the geometric parameter of the economizer is obtained with the experiment study. This formula is of enormous practical significance.It can be used to compare the extent of erosion for the staggered plain tube ecnomizers with different geometric parameters directly and it can also be regarded as a reference in the engineering application.