Abstract: As ocean exploitation has entered the era of full ocean depth, it is urgent to acquire mechanical properties of seabed sediments. Due to the complex marine engineering geological conditions, especially those in the deep ocean, it is rather difficult to collect high-quality undisturbed samples through conventional sampling techniques, and thus in-situ testing has become an only choice for submarine engineering survey. This paper aims to present a general introduction to the in-situ test methods, such as cone penetration test, vane shear test and full flow penetration test. And the factors that influence the in-situ test results are summarized, including water depth, sediment type and interpretation method. A deep sea exploration technology named "hadal lander technology" is introduced in details. A preliminary recommendation for development of in-situ measurement of sediment mechanical properties of full ocean depth is proposed.