Abstract: The piezocone penetration tests(CPTU)were performed in Lanyungang,China,and several in-situ test indexes such as undrained shear strength(Su),overconsolidation ratio(OCR) and coefficient of earth pressure at rest(K0) were calculated.The ionic chemistry examinations were also adopted.It was shown that the Fe3+ concentration was the obvious factor influencing on in-situ test index of Lianyungang marine clay.The Fe3+ existed as colloid in Lianyungang marine clay,which might influence the cementation between soil particles.More Fe(OH)3 colloid content could lead to light overconsolidation and influence the elastics characteristics of the clay.