Multibaseline InSAR is an effective extension of the traditional single baseline InSAR, which can provide highprecision DEM. Among all the reconstruction algorithms, Markov random fields based maximum a posteriori estimation (MRFMAP) is a robust and precise method. The hyperparameter estimation is a key step of this method which will affect the final DEM accuracy. In practice, the estimation of the hyperparameter is achieved by EM algorithm combined with Monte Carlo methods. In this paper, we utilize the multipletrial Metropolized independence sampler (MTMIS) instead of MetropolisHastings to realize Monte Carlo calculation. The experiment result validate that this improvement can improve the DEM accuracy finally. Moreover, we deduce the estimation variance of the EM step.