Simulation analysis of molding process for straw biomass was carried based on ANSYS. The mechanics mold was established according to its biology mechanism and chemical component, along with contact pairs. Then molding rules and relations between pressure and deformation were obtained through nonlinearity analysis. The analysis results showed that biomass molding under general condition process included three stages: loose, compaction, solidification, which combined the plastic deformation with the viscous deformation. The obtained results are well in agreement with experiment data.