[Objective] To explore the mechanism of seasonal responses of soil environmental factors to in-situ ecological remediation of crude-oil contaminated soil in Eastern Gansu Province of the loess plateau

in order to provide reference for the popularization and application of ecological restoration of soil plant microorganisms.[Methods] A combined remediation experiment using the indigenous crude-oil degradation bacteria agent and the native plant (Calendula officinalis) as materials had been conducted for in-situ ecological remediation of crude-oil contaminated soil for 285 days. The changes and seasonal responses to the in-situ ecological remediation of soil physicochemical property

enzyme activity and microbial-community property were investigated using conventional methods.[Results] (1) Soil TPHs degradation rate in summer (24.62%±3.96%) and fall (29.93%±1.94%) were higher than those in spring (3.82%±0.91%) and winter (9.24%±0.87%) during the process of in-situ ecological remediation. (2) There were obvious interactions between remediation treatment and seasonal variation with regard to soil physicochemical property and enzyme activity (p<0.05). Soil pH value

salt content and organic content were lower and soil nutrient were higher in fall in comparison with that of other seasons (p<0.05)

respectively. (3) Evenness index of soil microbial community was less in spring (p<0.05)

and its richness index was higher in summer (p<0.05)

as well as the Shannon-Wiener index was higher in summer and fall (p<0.05). (4) Nonmetric multidimensional scaling analysis suggested that the seasonal difference of soil TPHs degradation rate was strongly affected by the richness index (r2=0.706 3

p=0.002) and soil available phosphous (r2=0.615 7

p=0.005). (5) Variation partitioning analysis revealed that the most important combined environmental factor to determine the degradation rate of soil TPHs in cold season (spring and winter) was the interaction between soil physicochemical properties and enzyme activity (54%). However

74% of the soil TPHs variation in warm season was explained by soil physicochemical property

enzyme activity and soil microbial community property.[Conclusion] The low soil TPHs degradation rates in spring and winter were resulted from the low evenness index of soil microbial community and low soil enzymes activity; while richness index and the Shannon-Wiener index of soil microbial community

soil available P and ecological remediation effectiveness all resulted to the high soil TPHs degradation rate in summer and fall.