Calcium-dependent protein kinases (CDPKs) are pivotal signaling transduction enzymes in plants, especially responsive to diverse stress, including herbivory. In this study, through comprehensive analysis of CDPK gene family in upland cotton, we showed that GhCPKs are widely expressed in multiple tissues of cotton and positively respond to various biotic and abiotic stress. We developed a strategy for screening insect-resistant genes based on the CRISPR/Cas9 mutant library of GhCPKs. The library contains 82 members of the GhCPKs using 246 sgRNAs to generate 518 independent T0 plants. The coverage rate of target genes reached to 86.18%, the genome editing rate reached to 89.49%, and the editing heritability reached 82%. Through field insect bioassay, 14 GhCPK mutants resistant or susceptible to insect were identified. The most obvious insect-resistant mutant, cpk33/74 (simultaneously knocking out the homologous genesGhCPK33 and GhCPK74), was selected for further study. Oral secretions (OS) from Spodoptera litura induced a rapid influx of Ca2+ in cpk33/74 leaves, resulting in a significant increase in jasmonic acid (JA) content. S-adenosylmethionine synthase (SAMS) is an important protein involved in plant stress response, protein interaction experiments provided evidence of interactions between GhCPK33 and GhCPK74 with GhSAMS1 and GhSAM2, respectively. Additionally, silencing GhSAMS1 and GhSAM2 in cotton using VIGS resulted in decreased defense against S. litura. This study provides an effective strategy for constructing a mutant library of gene families in polyploid plant species and valuable insights into the role of CDPKs in the interaction between plants and herbivorous insects.