The invention discloses an associated protein for regulating and controlling round-leaf characteristics of cucumbers as well as a coding gene thereof and application thereof. An amino acid sequence ofthe protein is as shown in SEQ ID NO:2; protein kinase, which belongs to an AGC kinase family, of serine / threonine is coded by a PID gene; a coding gene of the protein is a base sequence as shown ina sequence table SEQ ID NO:1; guanine (G), at a site 1092bp, of the base sequence is substituted by adenine (A), Val (valine) at a site 346 of a coded amino acid residue sequence is mutated to be Met(methionine); the protein inhibits polar translocation of auxin, causes polar defect of auxin transport, has a blade edge smooth plant phenotype, has unapparent saw-tooth bugles, and has nearly roundleaves; a main root is not developed, and a main lateral root does not have obvious difference; male and female flowers are free of calyxes, and female flowers are not developed and the like. The geneand the protein can provide a basis for improving cucumber leaf type, increasing the yield, cultivating ideal plants and researching an auxin signal channel molecule regulation mechanism.