A promising quantitative method is the use of fluctuations of seawater silicon isotope compositions (δ30Siseawater) to estimate the silicon cycle and silicon isotopic budgets of both the marine and terrestrial systems in a pre-diatom ocean. However, a thorough global calibration of Phanerozoic δ30Siseawater, which is linked to continental tectonics and silicate weathering, has not been established. The silicon and oxygen isotope compositions of Darriwilian cherts (δ30Sichert and δ18Ochert, respectively) have considerable potential as proxies for δ30Siseawater and sea surface temperatures (SSTs), which can expand our understanding of the influence of continental tectonics and temperature changes on the Great Ordovician Biodiversification Event (GOBE). In this study, primary depositional and early diagenetic cherts were sampled from bedded chert, lump-shaped chert, nodular chert, and banded chert from five Darriwilian outcrops in the Kalpin and Yijianfang areas of the Tarim Basin in China. The preservation conditions of these cherts were assessed based on petrographic criteria such as the absence of calcite veins and fractures under macroscopic observation and the absence of aggregate chalcedony (CHA), microquartz (MQ), and cryptocrystalline quartz (MQC) using optical microscopy and scanning electronic microscopy (SEM). The SSTs and δ30Siseawater of Darriwilian seawater were reconstructed using the δ18Ochert and δ30Sichert of well-preserved cherts. Our results show that the SSTs were approximately 32 ± 5 °C in the early Darriwilian and approximately 30 ± 5 °C in the late Darriwilian. The δ30Siseawater was approximately +3.1‰ in the Kalpin and Yijianfang areas during the Darriwilian Stage. This is the first estimation of δ30Siseawater in the Darriwilian Stage, which provides a parameter for the global calibration of the δ30Siseawater of the pre-diatom ocean in the Phanerozoic Eon and validates the hypothesis that the pre-diatom ocean waters had higher δ30Si values than modern seawater. •A method of calculating the initial pore water Si isotope compositions was presented.•The sea surface temperatures of Darriwilian seawater were calculated.•The Si isotope compositions of Darriwilian seawater were estimated.