Background: There is a lack of consensus of operative time (OT) and estimated blood loss (EBL) for elderly patients based on the predicted risk of complications after posterior spine surgery. The purpose of this study was to evaluate the effect of age, OT, and EBL on the postoperative complication risk and to develop a simple sliding scale. Methods: We explored prospectively collected data of consecutive patients who underwent posterior spine surgery in seven tertiary referral hospitals from November 2013 to May 2016. Age (<70, 70–74, 75–79, 80–84, ≥85 years), OT (<2, 2–<3, 3–<4, 4–<5, ≥5 h), and EBL (<500, 500–<1000, 1000–<1500, 1500–<2000, ≥2000 ml) were categorized ranging from 1 (lowest) to 5 (highest). The association between the crude cumulative categories' number and the incidence of complications was analyzed. We further evaluated the association by re-categorizing the cumulative number into three groups (3–4, 5–10, ≥11). Results: Total of 2416 patients (median age: 70 years old) were enrolled and major complications were observed in 75 (3.1%) patients. Age, OT, and EBL showed similar odds ratio (1.18–1.19) as each category increased. The cumulative categories' number fitted the estimate complication risk (Hosmer–Lemeshow P = 0.87), and statistically significant trend was observed between predicted and actual complication rates (Cochran–Armitage test, P < 0.001). When cumulative categories' numbers were stratified into three groups, significant increasing trend of risk were observed (Mantel-Haenszel P < 0.001). Based on the categorical numbers, we proposed a simple sliding scale. Conclusion: Our data indicated that the risk of postoperative complication was associated with cumulative score based on increased age, OT, and EBL. A simple sliding scale was developed based on these factors, which may be useful to predict complication risk after posterior spine surgery.