Regarding the coral reef soft-soil at Tusdeer Port in Saudi Arabia，this paper analyzes the formation causes of coral reef soft-soil combining with the regional geological characteristics，and determines the engineering properties according to the results of laboratory test and in-situ cross plate test. The results show that the formation of coral reef soft-soil has regional characteristics. The gentle and serrated lagoon shallow basin landform are conducive to the deposition of fine particles. The distribution of soft soil is often discontinuous and relatively small scale. The carbonate content of soft soil is high，but there are regional differences. The proportion of silt in coral reef soft-soil is 56% to 79%，and characteristic properties of this soil are quite different from those of general coastal soft soil，river or lake soft soil. The cohesive force of coral reef soft-soil is 2 kPa to 5 kPa，which is lower than that of coast and delta soft soil，and the internal friction angle is 22°to 31°，which is higher than that of coast and delta soft soil. In the range of depth from 2 m to 5 m，the strength of in-situ vane of coral reef soft-soil is about 20 kPa，and the sensitivity is 1.5，which belongs to low sensitive soft soil. The coral reef soft-soil has poor engineering properties，which are harmful to the project. The adverse influence of coral reef soft-soil site on project should be fully considered，and the complexity of geologic conditions should be carefully evaluated.