The invention relates to an in-situ preparation method of ceramic whisker/nylon composite material. The method includes that ceramic whiskers are mixed with water, polymer monomers and molecular weight regulator in a certain proportion and then put in a polymerization autoclave; the mixed substances are pre-polymerized for 1-14 hours under the conditions of 200-260 EDG C and 0.6-3.2 MPa in the polymerization autoclave, then polymerized for 0.5-4 hour(s) under constant pressure after vapor is discharged, and finally polymerized for 0.2-2 hour(s) under the conditions of 220-300 DEG C and 200-6000Pa after pressure is lowered; the nylon composite material enforced by ceramic whiskers is directly prepared. Compared with the traditional screw extrusion melt blending technology and the constant-pressure in-situ polymerization technology, the method of the invention realizes even dispersion of the whiskers in the composite material and great improvement of enforcing and toughing effect of thewhiskers.