Abstract: The deep-sea diatomite is a kind of siliceous ooze of deep-sea biodiatom origin, which is featured with very high water content and low strength. A rheological model in fluid mechanics is used to describe the strength of diatomite, and the relationship between the undrained shear strength of diatomite and the shear strain rate is established through the rheological tests. It is found in the tests that the sensitivity of diatomite cannot be ignored. When the optical cables are laid on the deep-sea diatomite, the cable settlement needs to be estimated reasonably. The interaction between the optical cables and the diatomite is explored using the large-deformation finite element approach, in which the effects of strain rate and strain softening are considered. Based on the numerical results, the factors affecting the penetration resistance of cables are discussed, while the cable settlements against a variety of sensitivities are investigated. The settlement ranges of two typical armored optical cables on diatomite are determined.