The invention relates to a high-temperature low-density cement and applications thereof, belonging to the field of building materials. The high-temperature low-density cement provided by the invention has excellent high temperature resistance and comprises the following components in percentage by weight: 30%-70% of cement substrate, 14%-40% of lightening material, 14%-30% of high-temperature strength stabilizer and 0.02%-0.10% of high-temperature retarder, wherein the high-temperature retarder is organic acid sodium salt, and the high-temperature strength stabilizer material is one of micro silicon and silicon powder or the combination of micro silicon and silicon powder. The cement has the characteristics of simple construction processes, high pulping rate, excellent high temperature resistance and the like, can be applied to special environments such as oil well cementing and the like, and can obviously improve well cementing quality and crude production rate. When the cement of the invention is used for well cementing operation and high-temperature oil production operation, the well cementing construction performance can be ensured, and the unabated performance of the strengthof the cement stone at high temperature can be ensured.