To elucidate the seasonal variations in soil salinity and its driving factors,and to explore the effects of planting Suaeda glauca and straw mulching on soil desalination and salinity controlling, a field experiment was conducted in extremely heavy saline soil of coastal areas in Rudong, Jiangsu Province. There were four treatments: control (bare land,CK),planting S. glauca (PS), straw mulching A (at 15 t·hm~(-2),SM-A),straw mulching 2A (at 30 t·hm~(-2),SM-2A). Climate factors (including rainfall,atmospheric temperature,sunshine duration,and atmospheric evaporation) and soil salinity dynamic changes were determined from May 2014 to May 2015. Results showed that: (1) The seasonal variation of soil salinity was obvious in the bare ground (CK),with the lowest (8.69 g·kg~(-1)) during June-August and the highest (26.66 g·kg~(-1)) during September- December. The changes of soil salinity in topsoil (0-20 cm) were more intense than that in subtopsoil (20 - 40 cm),with the changes in sub-topsoil having somewhat time lag compared the topsoil. (2) Soil salinity in CK treatment had a significantly linear correlation with the cumulative rainfall and evaporation-precipitation ratio of the fifteen-day before sampling. The results from multifactor and interphase analysis indicated that the increases of rainfall would promote soil desalinization. The rise of atmospheric temperature could exacerbate soil salt accumulation in surface soil. The interaction between rainfall and atmospheric temperature would have a positive effect on soil salt accumulation. (3) PS treatment did not alter the seasonal variation in soil salinity,but it reduced soil salinity in topsoil. (4) In SM-A and SM-2A treatments,the relationship of soil desalinization rate (%,Y) and treatment time (days,X) was expressed as Logistic curve equation. Moreover, the soil desalination rate was over 95.0% in the topsoil after 90-100 days of straw mul-ching treatment and was over 92.0% in sub-topsoil after 120 days of straw mulching treatment. The soil salinity in SM-A and SM-2A treatments fluctuated below 0.60 g·kg~(-1) and 1.00 g·kg~(-1),respectively in topsoil and sub-topsoil. Considering the desalination and economic costs,a suitable amount of straw mulching (such as 15 t·hm~(-2)) before rainy season was recommended,which would promote the soil desalinization and reclamation in extremely heavy saline soil of coastal areas.