Considering change in negative vacuum pressure with time, the governing equations and the corresponding solution conditions for consolidation of the composite ground with T-shaped deep cement mixing (TDM) columns under vacuum preloading were derived. Based on one dimensional consolidation theory of a double-layer soil ground, the average excess pore water pressures within the improved zones and the surrounding soil were obtained by the functional transformation of the consolidation equations and solution conditions. The overall average consolidation degree of the composite ground with TDM columns was presented. Then, the rationality of the proposed solutions was verified by comparison with the numerical simulation results. Finally, the influence of the replacement ratio of the column, the column cap size, the stiffness of the surrounding soil and the vacuum loading parameter on the consolidation rate of the composite ground was investigated using the proposed solution.The results indicate that the consolidation rate of the composite ground increases with increasing the replacement ratio of the column , the height of its cap and the constrained modulus of the soil under the column cap. The consolidation is accelerated with increasing the radius of column cap in the early stage of consolidation, but it has insignificant influence in the later stage of consolidation process. The vacuum loading process has little effect on the consolidation of the composite ground.