Medium high temperature early strength agent for oil well cement

The invention discloses a medium high temperature early strength agent for oil well cement. The medium high temperature early strength agent for the oil well cement comprises the following components in part by weight: 1.2 to 2.8 parts of sodium thiosulfate, 0.2 to 2 parts of basic aluminum chloride, 0.2 to 0.6 part of sodium nitrate, 0.2 to 1 part of microsilicon and 0 to 0.2 part of calcium aluminate. The medium high temperature early strength agent for the oil well cement has the beneficial effects that: the early strength of cement stone can be improved obviously at high temperature on the premise of not influencing the thickening time; the problem that the early strength of the cement stone is developed slowly at medium high temperature is solved; the medium high temperature early strength agent has high compatibility with other additives; and at medium temperature, water loss of cement paste can be controlled, the adding amount of a fluid loss agent is reduced, and the cost is saved.