A study on a new lithium salt accelerator was conducted in this paper aiming at the low temperature environment in deepwater cementing. The acceleration mechanism and comprehensive performance of the lithium salt accelerator were thoroughly discussed. Results show that the lithium salt accelerator can accelerate the low-temperature hydration rate of C3S and C2S by speeding up the rupture of protective hydration film and shortening the hydration induction period, and thereby significantly shortens the low-temperature thickening time and the 48-240 Pa transition time for the static gel strength of oil well cement slurry, dramatically improves the compressive strength at low temperatures and shows no effect on the initial consistency of cement slurry. The lithium salt accelerator shows favorable low-temperature early strength accelerating property and has no effect on the types of hydration product, which still remains the same with that of conventional oil well cement, namely the calcium silicate gel, Ca(OH)2 crystal and a small amount of ettringite AFt crystal. But the micro-structure of the system with the lithium salt accelerator is more compact than that of conventional set cement.