The resource potential of in-situ conversion of shale oil is enormous，and it is a strategic replacement resource for China’s oil and gas industry. However，extreme high temperatures under low maturity shale oil in-situ conversion conditions can lead to a decline in the strength of hardened cement. The influence of modified material sodium hexametaphosphate on the hydration behavior of aluminate cement and the application performance of cement slurry at the high temperature environment of 650 ℃ was systematically studied，and its macro performance and microstructure were deeply explored. low field nuclear magnetic resonance analysis and testing technology showed that the sodium hexametaphosphate had a significant retarding effect on the initial hydration behavior of aluminate cement and could effectively improve its rheological properties. In addition，at the temperature of 50 ℃， addition of sodium hexametaphosphate could significantly reduce the permeability of hardened aluminate cement，at the same time， which had no significant impact on the strength. After treatment at the temperature of 650 ℃，the maximum compressive strength of was 47.19 MPa by adding 5% sodium hexametaphosphate to modify hardened aluminate cement. Simultaneously，before and after treatment at 650 ℃，the hydration products of aluminate cement slurry underwent significant transformation，the C₃AH₆ and AH₃ converted into C₁₂A₇ and CA mainly. C₃AH₆ and AH₃ underwent thermal decomposition mainly during the period of 180—400 ℃. the pore size distribution of mercury intrusion showed that the pore size range of clean hardened aluminate cement and 5% sodium hexametaphosphate modified hardened aluminate cement was mainly between 100 and 1000 nm，and the pore size of both types of cement stones increased due to the transformation of crystal form after high-temperature treatment at the temperature of 650 ℃.