Abstract: In order to weave the desired fabric with varied weft density, affected factors of reed-base’s front extreme position of four-bar beating-up linkage are analyzed. Elastic dynamic model for four-bar beating-up linkage of a air-jet weaving machine is established. Influences of weaving resistance and loom speed on the reed-base’s elastic displacement at front extreme position are studied. Curves of reed-base’s elastic displacement versus weaving resistance and reed-base’s elastic displacement versus loom speed are abtained and verified with experiments. The results show that influence of weaving resistance on reed-base’s elastic displacement is small and influence of loom speed on reed-base’s elastic displacement is slightly large, but both couldn’t change the weft position at beating-up end obviously.