SGP-1 is a key enzyme responsible for the elongation of amylopectin side chains in wheat endosperm, and its loss of function increases amylose content, making SGP-1 a target gene for developing high-amylose wheat through marker-assisted selection. In this study, molecular markers developed from the genomic DNA sequences of SGP-1 were used to screen a Yannong 18 radiation-induced mutant library, and sgp-A1 and sgp-D1 deletion mutants were identified. SDS-PAGE confirmed the absence of SGP-A1 and SGP-D1 proteins, and whole-exome sequencing revealed large DNA fragment deletions encompassing SGP-A1 and SGP-D1, respectively. Using Kanto 79 as the donor of sgp-B1, we pyramided the three null alleles via a double-crossing scheme and developed a novel high-amylose wheat germplasm with SGP-1 deficiency, which exhibited the typical characteristics of SGP-1 deletion mutants. Through agronomic trait evaluation, the optimal high-amylose wheat line F2301 was selected. The amylose content of F2301 was increased from 25.2% to 29.2%, and the resistant starch content was increased from 1.25% to 2.83%, providing a valuable material foundation for functional wheat breeding.