Science achievement and the factors related to it are frequently discussed in science education community. However, less researchers tend to consider student achievement in other subjects, especially reading and mathematics as included in the "Programme for International Student Assessment" (PISA). This research examined the relationship between student achievement in reading, mathematics, and science. Based on the theoretical analysis, we proposed several hypotheses that students' reading achievement can influence their mathematics achievement, reading achievement can influence science achievement, and mathematics achievement can influence science achievement, and we can use a triangular model to represent such relationship. To test the hypotheses, we used the dataset of PISA 2018 as the data source, selected 12,058 Chinese students as the participants, and employed Structural Equation Modelling (SEM) for data analysis. The results confirmed the hypotheses. Our findings indicated that reading and mathematics were important predictors of science achievement, and the effects of reading significantly exceeded mathematics. We, therefore, concluded that reading should be more important than mathematics and received with more concern in science learning. The inconsistency of the results in this research with previous works is also discussed below.