Increasing the yield of rice has always been one of the primary purposes of rice breeding. However, panicle degeneration, a complex characteristic regulated by many genes and commonly encountered in rice production, seriously reduces yield. In this study, we obtained a new apical panicle degeneration mutant named ym48, which induces a marked degeneration rate and reduces grain yield in rice. Cellular and physiological analyses revealed that the apical panicle in ym48 undergoes programmed cell death, accompanied by the accumulation of higher levels of peroxide. Next, the OsCAX1a gene, which is responsible for Ca ²⁺ transportation, was identified, and a highly conserved A to G substitution was noted at the 190 ^th nucleotide in ym48, which seriously damaged Ca ²⁺ transport. Through hydroponics assays and Ca ²⁺ quantification, we found that Ca ²⁺ transportation and distribution from the underground part to apical tissues was blocked and overaccumulated in mutant stems. In general, this Ca ²⁺ deficiency mediated by OsCAX1a induced peroxide accumulation and resulted in programmed cell death in the apical panicle of the ym48 mutant. Our results demonstrate the essential role of OsCAX1a in Ca ²⁺ transportation and distribution, laying a foundation to further explore the genetic and molecular mechanisms of panicle development and differentiation in rice.