Soil samples with different contaminant concentrations were stabilized by different added doses of cement. Unconfined compressive test results were used to analyse the influence of curing time, diesel content and cement addition ratio on the strength formation process. Micrographs of samples were used to analyse the deterioration in soil properties caused by diesel and the stabilization effect of cement. The results showed that different combinations of curing time, diesel and cement content led to different strength increase processes. For unstabilized contaminated soil, the time needed to finish the deterioration brought about by diesel in slightly contaminated samples was longer than that in heavily contaminated samples. For stabilized contaminated soil, the strength formation process in samples with low diesel contents and low cement addition ratios was faster than that in samples with high diesel contents and low cement addition ratios, and the strength formation process of samples with high cement addition ratios was slow. A higher strength increase was obtained in slightly contaminated samples stabilized by cement at a low addition ratio. The amount of fine particles increased in contaminated samples, and the stabilized contaminated samples had a denser aggregated structure and a higher content of large aggregations compared with the original sample.