Objective To establish a new risk score model for the diagnosis of posterior circulation ischemia（ PCI） related vertigo， and to determine the optimal cut-off values and validate their diagnostic value in PCI-related vertigo in the elderly. Methods This study was conducted in two steps. Firstly， a risk score model was developed using multifactorial logistic regression analysis according to regression coefficient values in 380 PCI-related vertigo patients and 380 control patients matched according to age and sex. It was then validated in 149 PCI-related vertigo patients and 328 control subjects. Receiver operating characteristic（ ROC） curve was applied to analyze the diagnostic efficacy of the score model， ABCD2 and Essen scoring systems to PCI related vertigo. Results Multivariate logistic regression analysis showed that 13 factors including 4 kinds of medical history（ hypertension， diabetes， ischemic stroke and hyperlipidemia）， 6 kinds of symptoms（ diplopia， dysarthria， choking on water， impaired hearing， unilateral limb weakness， and tinnitus） and 3 kinds of physical signs（ limb sensory loss， limb ataxia and gait ataxia） were the influencing factors of PCI related vertigo（ P＜0.05）， and included in the final diagnostic risk model， with score ranging from -6 to 32. The higher the score was， the more likely the diagnosis was. Based on the PCI risk score， patients were divided into 3 subgroups： low-risk （-5 to 0 points， risk is less than 18.4%）， intermediate-risk（ 1 to 10 points）， and high-risk（ ≥11 points， risk is greater than 80.2%）. According to Youden index， the optimal cut-off point of PCI scoring system was 4 points， with a sensitivity of 92.2% and a specificity of 58.7%. The area under the ROC curve of PCI scoring system was 0.846（ 95%CI：0.794 to 0.898）， which was significantly higher than that of ABCD2［ 0.752（ 95%CI：0.668 to 0.836）］ and Essen scoring system［ 0.659（ 95%CI：0.569 to 0.748）］（ P values of Delong test were 0.009 and 0.001， respectively）. Conclusions The PCI scoring system was superior to the ABCD2 and Essen scoring systems in diagnosing PCI-related vertigo. A score of 4 is the diagnostic threshold for this scoring system， but elderly patients with a PCI risk score above 0 should undergo further investigation.