Abstract: Aiming at the problem of low interfacial adhesion strength between ultra-high molecular weight polyethylene (UHMWPE) fiber and matrix, ultrasonic treatment and chromic acid solution oxidation compound process were used to perform surface modifications of UHMWPE fiber, and the modified fiber was added into natural rubber (NR) to prepare short-cut UHMWPE fiber/NR composites. The results show that the compound modification process could effectively increase the roughness and oxygen-containing group contents on surface of fibers, and the optimum modification conditions are: the chromic acid etching solution is prepared by mixing potassium dichromate, distilled water, and sulfuric acid with 7:12:150 mass ratio, and put the chromic acid solution which is filled with a certain quality UHMWPE fiber into ultrasonic cleaning instrument to oxidize for 5 min at 35 ℃, and the ultrasonic frequency is 100 kHz. Then, the as-prepared fibers were added into NR with mass ratio ranging from 0 to 6:100. Compared with the pure NR samples, with the increase of short fiber content, the tensile strength of composites decreases, mostly by 50%, the hardness increases, mostly by 96%, the tear strength first increases then decreases, and reaches mostly by 49% with mass ratio 5:100 between UHMWPE fibers and NR.