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In the life cycle of apple, it will suffer a variety of abiotic stresses, such as iron stress and salt stress. bHLH transcription factors (TFs) play an indispensable role in the response of plants to stress. In this study, a new <i>bHLH</i> gene named <i>MxbHLH18</i> was separated from <i>Malus xiaojinensis</i>. According to the results of subcellular localization, <i>MxbHLH18</i> was localized in the nucleus. Salt stress and iron stress affected the expression of <i>MxbHLH18</i> in <i>Malus xiaojinensis</i> seedlings to a large extent. Due to the introduction of <i>MxbHLH18</i>, the resistance of <i>Arabidopsis thaliana</i> to salt, high iron and low iron was significantly enhanced. Under the environmental conditions of high iron and low iron, the overexpression of <i>MxbHLH18</i> increased many physiological indexes of transgenic <i>Arabidopsis</i> compared to wild type (WT), such as root length, fresh weight and iron content. The high level expression of <i>MxbHLH18</i> in transformed <i>Arabidopsis thaliana</i> can not only increased the content of chlorophyll and proline, as well as increasing the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT); it also reduced the content of malondialdehyde (MDA), which was more obvious under high salt conditions. In addition, the relative conductivity, H₂O₂ content and O²⁻ content in transgenic <i>Arabidopsis</i> decreased under salt stress. Meanwhile, <i>Mx</i><i>bHLH18</i> can also regulate the expression of downstream genes associated with salt stress (<i>AtCBF1/2/3</i>, <i>AtKIN</i><i>1</i> and <i>AtCOR15a/b</i>) and iron stress (<i>AtIRT1</i>, <i>AtFRO2</i>, <i>AtNAS2</i>, <i>ATACT2</i>, <i>AtZIF1</i> and <i>AtOPT3</i>). Therefore, <i>MxbHLH18</i> can actively promote the adaptability of plants to the growth environment of salt and low and/or iron.