Based on systematic analysis on rock magnetism and grain size, this paper studies the topsoils of the loess region of Tianshan Mountains and the Loess Plateau in northwestern China. Their magnetic characteristics indicate that the main magnetic minerals of these topsoils are magnetite, maghemite, hematite and lepidocrocite or goethite. The grain size of magnetic minerals in Tianshan topsoils is generally much coarser; mostly within range of multi-domain (MD). Hard magnetic minerals in Tianshan topsoils are higher than that of Loess Plateau. The magnetic susceptibility of topsoils from Loess Plateau shows a good positive relation with frequency dependent susceptibility. Climate condition, such as temperature and precipitation, especially the latter one, is considered as the major factor effecting susceptibility enhancement in the Loess Plateau. Tianshan topsoil contains a very small amount of ultrafine magnetic grains produced during pedogenesis, which has very limited contribution to the susceptibility enhancement. Tianshan topsoils generally show a characteristic of less weathering or weak pedogenesis, aeolian coarser grains, therefore play an important role in mechanism of magnetic susceptibility enhancement. Frequency dependent susceptibility shows a close relation with mean annual precipitation (MAP) in all studied areas. However magnetic susceptibility demonstrates difference with MAP in various regions: showing positive correlation in the central Loess Plateau (studied area); but negative relation with MAP in Tianshan area. Therefore, great care should be taken when explaining environments using magnetic susceptibility values from different regions.%本文对黄土高原和天山黄土区表土进行系统的岩石磁学和粒度测试分析,探讨了表土磁性特征及其环境意义,结果表明表土中的强磁性矿物均为磁铁矿和磁赤铁矿,弱磁性矿物为赤铁矿和纤铁矿或针铁矿,黄土高原黄土地层中的磁赤铁矿至少有部分属于风积成因.黄土高原表土中磁化率与频率磁化率呈良好的正相关,气候作用是主导黄土高原表上磁化率增强的主要因素.天山表土的磁颗粒比黄土高原粗,以多畴为主.近物源,粗粒度,弱成土(即成壤作用对磁化率的贡献小)是天山表土基本特点,并且风力强弱是影响该地区磁化率变化的主要因素.频率磁化率在小同地区显示出与年均降水量较明显正相关关系；而磁化率与年均降水量的相关关系在不同地区、不同气候条件下表现不同:在黄土高原中部(本研究区)显示正相关；而在伊犁地区表现为反相关.因此应用磁化率解释环境时要注意其区域性.
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