Prestress loss of anchor cable should not be neglected in engineering construction. The cause of prestress loss is usually related to engineering site condition. The saturated silty sand is more complicated and sensitive than other geological conditions

which is more likely to cause prestress loss. Through real-time monitoring of anchor prestress of a deep foundation pit in Langfang city

combining with the engineering environment

factors influencing on variation of anchor prestress are analyzed. The results show that the process of construction

tension and environmental factors affect the variation of prestress. The most obvious impact is the excavation process; and the maximum rate of variation of prestress value is 79.1%; instantaneous unloading causes values of prestress loss between 22.8% to 59.2%. The influence of construction process is most obvious. Experience for similar geological engineering construction is provided through the research and analysis of variation law of anchor prestress.