The invention relates to a high-temperature high-pressure tensile stress strain system of oil well cement. The system comprises a cement tensile test assembly, a power supply and pressure control unit, a temperature control unit, a signal control processing unit and pipelines. By adopting the system of the invention, the temperature and the pressure for the bottom maintenance can be simulated, the tensile stress strain of the oil well cement can be continuously measured under conditions of the temperature and the pressure, and the temperature pressure curve and the tensile stress strain curve are recorded. The system and the measure method of the invention are in favor of the intuitional test, the comparison of tensile resistances of different cement paste systems and the design of the cement paste formula, so cement paste systems which can satisfy on-site construction requirements are obtained.