[目的]探讨选择压力与核苷酸替代率的关系。[方法]采用统计学方法分析高粱、玉米中部分核基因、细胞器基因的同义替代率、非同义替代率以及2者之间的比值,并对一些相关功能基因进行对比分析。[结果]相关功能基因在核与叶绿体中所受的纯化选择压力相近,在线粒体中则较低。高粱、玉米核同源基因间及核中不同功能基因间核苷酸替代的差异主要由非同义替代的差异造成。[结论]选择压力影响不同功能基因、不同物种的分子进化速率,而核与细胞器基因间进化速率的差异与选择压力间并无直接联系。 [Objective] To explore the relationship between selection pressure and nucleotide replacement rate. [Method] Statistical analysis was used to analyze the synonymous substitution rate, non-synonymous substitution rate and ratio between some nuclear genes and organelle genes in sorghum and maize, and comparative analysis of some related functional genes. [Result] The related functional genes had similar pressure on purification selection in nucleus and chloroplast, but lower in mitochondria. Differences in nucleotide substitutions between sorghum, maize homologous genes and among different functional genes in the nucleus are mainly caused by differences in non-synonymous substitutions. [Conclusion] The selection pressure affected the molecular evolution rate of different functional genes and different species. However, there was no direct correlation between the differences in the evolution rate of nuclei and organelles and the selection pressure.