【Objective】This study is oriented to acquire theoretical values (or baseline value) of As and Hg in purple soils different in developmental stage, to understand migration and accumulation processes of the elements in the soils, and to provide an accurate and reliable basis for evaluation of heavy metal pollution of the soil. 【Method】Samples of the purple parent rock of the Jurassic Shaximiao Formation (J₂s) and various soils species derived from the same parent rock, but different in developmental degree were collected according to the traditional nomenclature in Hechuan District of Chongqing, for analysis to determine and verify development degrees of the soil with the "titanium value" method of soil; To measure total As and total Hg in the soils, to build up environmental geochemical baseline models for As and Hg in the soils of the gray brown purple soil genus in the purple soil group, and to define the chemical baseline values for each soil along the developmental line. 【Result】Results show that in terms "titanium value", the soils followed an order of parent rock > stony sub-soil > half sand half mud > big-eye mud > purple yellow mud, which reflects that the sequence of the soils in development degree coincides with the traditional order of the soils along the soil development line and that the soil sampling complied with the requirements of the study; The environmental geochemical baselines of As and Hg in the soils were found both on the trend of slight accumulation with deepening soil development, in terms of baseline value of As, the soils followed an order of parent rock < stony sub-soil < half sand half mud < big-eye mud < purple yellow mud, while in terms of baseline value of Hg, the soils followed another order: parent rock < stony sub-soil < half sand half mud < purple yellow mud -1,) and Hg (29.0 μg kg^-1) in the deeply developed soil be used as the reference for evaluation of soil pollution in the soils of the gray brown purple soil genus of the neutral purple soil subgroup in Chongqing area.