Abstract: Ocean engineering has moved towards the deep sea. But in-situ testing technology for undrained shear strength of deep sea shallow sediments is not yet mature. This paper develops a multi-probe in-situ test system that can evaluate the soil mechanical properties of deep-sea shallow sediments. It includes CPT, Ball Full-flow Penetrometer and VST to achieve a rapid, accurate and intelligent evaluation of the soil mechanical properties of deep-sea shallow sediments. Further the resistance coefficient of CPT is determined with CEL large-deformation numerical analysis method and the full-scale geotechnical model test, and the resistance coefficient of Ball Full-flow Penetrometer is given by the centrifugal model test. Then the undrained shear strength evaluation method of deep sea shallow sediments is improved. On this basis, the undrained shear strength test intervals suitable for each of the instruments are discussed. Results indicate that for the evaluation of the deep-sea shallow saturated soft clay undrained shear strength, the recommended penetration coefficients of CPT and Ball Full-flow Penetrometer are respectively 9.5 and 11.1.