A genetically-modified rat having a PKHD1L1 gene with a point or other mutation and a construction method thereof are disclosed. A CRISPR/Cas9 system knocks the PKHD1L1 gene into a mouse source, and a codon changes from TTA to TCA to construct the mutant PKHD1L1 gene. The genetically-modified rat can be applied to epilepsy pathogenesis studies and design and testing of new anti-epileptic drugs. Methods for detecting abnormal cortical excitability and detecting an epileptic phenotype of an animal can use the genetically-modified rat. A somatosensory evoked potential is used to detect whether the genetically-modified rat has an abnormal cortical excitability phenotype, so as to confirm whether the rat can be a successful model for testing anti-epileptic drugs. The method can detect abnormal cortical excitability and verify the effectiveness of anti-epileptic drugs or treatments.