Cotton production plays an extremely important role in the local economy, and the income from cotton cultivation is one of the major financial sources for farmers in Xinjiang. The cotton production of Xinjiang that is the biggest cotton production base in China has been developing rapidly since the 1990s, and now the sowing area, yield per hectare and total yield of cotton all rank first among the provinces in China. To better understand effect of long-term monoculture of cotton on temporal and spatial variation of 5 soil microelement (Total Mo, Total Cu, Total Zn, Total Mn, Total Fe) contents in the field, cotton fields different in cultivation history (1, 5, 15, 20 and 30 years) were selected in South Xinjiang for the study on relationship between soil microelement contents and history of continuous cropping. Results show that with the cropping going on, in the plow layer (0~20cm) total Mo decreased, showing a unitary negative linear relationship, while total Cu, total Zn and total Mn first rose up, peaking in year 7~10, 10~12 and 17~18, separately and then declined, dropping back in year 14~17, 20~22 and 32~34 separately to the initial value, showing a quadratic functional relationship. In the sublayer (30~50cm), the microelements decreased significantly, showing a unitary negative linear relationship with the time and demonstrating a tendency of long-term monoculture leading to deficiency of microelements in the layer. And in the botton layer (50~60 cm), the totals of these microelements increased to a various degree, but did not show any apparent functional relationship with the time. With the monoculture going on, the lower the microelement in content in the soil layer (0~60cm), the more apparent the fall of its content, with Mo in particular, which was followed by Zn, Cu, Mn and Fe. Therefore, in fields that have long been cultivated with cotton continuously, it is essential to supplement microelement fertilizers, like Mo, Zn and Cu, and in addition perform deep tillage so as to raise microelement contents in the sublayer.