The invention belongs to the catalytic technical field, and discloses a carboxymethyl hemicellulose supported palladium catalyst, a preparation method therefor and an application thereof. The preparation method for the catalyst comprises: adding carboxymethyl hemicellulose and a palladium salt into a solvent to obtain a mixture; reacting the mixture for 4-24 hours at 20-60 DEG C; and filtering, washing and drying the mixture to obtain the carboxymethyl hemicellulose supported palladium catalyst. An application process of the catalyst in catalyzing Heck reaction comprises: adding the carboxymethyl hemicellulose supported palladium catalyst, benzene halide, olefin and acid-binding agent into a solvent, and carrying out reaction for 4-12 hours under an oil bath of 60-140 DEG C; and filtering to remove the catalyst, adding deionized water into filtrate to extract, getting an organic phase, adding the organic phase into anhydrous magnesium sulfate to dry, filtering and carrying out distillation under reduced pressure to remove the solvent, and carrying out column chromatography purification to obtain a catalytic synthesis product. The catalyst disclosed by the invention has the advantages of good catalysis effect, convenience in separation and low cost, and has a good application prospect.