JKN-EA-401 expanding additive for oil well cement is of the cement hydration products, which can compensate for the grout (stone), shrink and produce volume micro-expansion. It is conducive to anti-channeling, compress cement porosity and improve the pores’ distribution, thus to achieve the goal of improving strength and reducing the permeability rate. And in restricted state, enhancing the product’s prestress and improving the bond strength of cement is good for preventing corrosion of the cement and casing pipes, and controlling loop current. JKN-EA-401 has a good compatibility with other additives, and does not affect the other properties of slurry. It has a wide scope of temperature allowance (25 ~ 150 ℃) and a good performance on salt tolerance.