Cement soil mixed piles are widely used in irrigation works， municipal road projects and urban infrastructure projects due to its advantages of convenience to construction， little pollution to environment， flexible arrangement and economic efficiency. This paper takes the extra large foundation pit support of Foshan new town CBD as the background and analyses the factors affecting the engineering characteristics of cement soil based on themicroscopic action mechanism between cement and soil，which include cement content， water content， age of cement and properties of soil. And strength distributing rule of cement soil is obtained through indoor unconfined compressive strength tests，where the control variables are cement content， comprehensive water content and age of cement. The test results show that the unconfined compressive strength of cement soil increases with the increase of cement content and age， and decreases with the increase of comprehensive water content. Finally，this paper deduces the comprehensive coordination parameter formula for the construction of cement soil mixed method according to the reasonable construction technology parameters， including field mix proportion of cement soil，rotating speed of stirring shaft， lifting and sinking speed of stirring shaft and times of duplicate stir.