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The principle of Particle Swarm Optimization (PSO) and Homotopy Optimization (HO) is introduced. For the purpose of improving the local-searching efficiency of the PSO，HO-PSO is presented by combining the PSO with HO. New space homotopy curve produced by homotopy particle function directs the particle’s local optimization. For comparison，the methods of HO-PSO, PSO and FEM(Finite Element Method) are used to calculate the tunnel parameter inversion of the Shuibuya Project on the basis of the measured displacements. The result shows that HO-PSO takes smaller time compared with PSO and FEM in a same precision level, and the calculated values are in good agreement with the measured values，which also indicate that the HO-PSO can be well applied to the displacement back analysis in tunnel engineering.

Based on the property that micro-cells strength is consistent with lognormal distribution function, this paper presented a new statistical damage softening constitutive model simulating the full process of strain softening for rock. Through discussing the characteristics of random distributions for rock micro-cells strength, lognormal distribution assumption is tested by Kolmogorov-Smirnov test in statistics, and the reasonable method of geometry boundary condition is selected to determine model parameters that can be easily applied to the situations under different complex conditions. Gabbro experiment comparative analyses show that the new damage softening constitutive model is rational and convenient in engineering.