The invention belongs to the field of biological medicine and particularly discloses high-strength composite hydrogel and a preparation method thereof. The high-strength composite hydrogel is prepared by simultaneously bonding polyacrylamide to the surfaces and in the ducts of nanoscale silicon dioxide molecular sieves. The preparation method includes: taking the nanoscale silicon dioxide molecular sieves, acrylamide and an ammonium persulfate aqueously solution, and stirring to obtain a turbid solution; evenly dispersing in an ultrasonic manner, vacuumizing, centrifuging, taking out sediments, and drying to obtain composite molecular sieves; evenly mixing the prepared composite molecular sieves with an acrylamide aqueous solution, vacuumizing, heating to 75-85 DEG C, and performing constant-temperature reaction for 30-40 minutes to obtain thick liquid; placing the thick liquid into a die, adding an N,N-dimethyl bisacrylamide aqueous solution, and heating at 50-60 DEG C for 7-8 hours to obtain the composite hydrogel. The high-strength composite hydrogel is good in mechanical performance, and the preparation method of the high-strength composite hydrogel is easy to operate.