In this investigation, hydrogen sensors were designed based on multi-walled carbon nanotubes (MWCNT) and Pd loaded on WO3 nanosheets by means of hydrothermal synthesis and impregnation reduction. First, WO3 with different morphologies were synthesized, including zero dimension (0D) nanoparticles, one dimension (1D) nanowires and two dimension (2D) nanosheets. After testing, the 2D-WO3 material was selected as the substrate material to form final Pd-MWCNT/WO3 composites. Outstandingly, Pd-MWCNT/WO3 sensor exhibited greatest sensitivity with high response value (371.13), fast response/recovery time (1/4 s) to 1000 ppm hydrogen at 175℃, excellent selectivity and reproducibility. Furthermore, the corresponding hydrogen sensing mechanism was proposed combining with DFT calculation of hydrogen adsorption energy. This was the first report on designing a novel ternary Pd-MWCNT/WO3 composites sensor applied to hydrogen detection and the first time to calculate the hydrogen adsorption energy of Pd-MWCNT/WO3.