Abstract: In this paper, a certified reference material (CRM) for phosphorus in isooctane (GBW11211) was developed to meet the national standard for measuring the content of phosphorus in light oil. The CRM was prepared with isooctane and phosphorus element standard hydrocarbon oil as raw materials, and inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES) were used as the characterization methods for the CRM, which were jointly characterized by several laboratories, and the homogeneity and stability of the CRM for elemental phosphorus in isooctane were evaluated. The results show that the certified value of the CRM of the phosphorus component in isooctane is 0.44 mg·kg⁻¹, with an extended uncertainty of 0.05 mg·kg⁻¹ (k =2), and the validity period is 36 months. The CRM can be used for quality control and method verification of related oil products.