Abstract: The coefficient of secondary compress ion C_a is investi gated in the long-term odometer tests. All the samples are made f rom the reconstituted Shanghai soft soils. The test condition includes differe nt stress history, different loading duration and different stress ratio.The ratio of C_c/C_a for Shanghai soft soil is got through the test. The reason why the C_a changes in some conditions is also explained in this paper by inducing the e₀ and e_p concept.