This paper provides an idea of statistics approach about the quality control for Cement Deep Mixing (CDM). Patimban Port Development Project (I) has a large construction area, then total 1.4 million m3 of CDM was installed. In addition, it was observed that the seabed profile could be clearly separated into 3 different types of soil layers and there was the organic clay in the middle layer. Considering the unique soil profile and the presence of the organic soil, the slag cement was selected for CDM construction. The cement factor was varied toward the depth direction for the economical construction purpose. In the middle of construction period those cement factors were adjusted after reviewing the result of Unconfined Compressive Strength (UCS) Test and the summary of percent failure. Percent failure means the percentage of specimens out of all tested ones whose the strength is less than the design. Not only histogram but also this percent failure helped us to decide the cement factor during the construction.