Background This study aimed to establish an effective and practical prognostic index for esophageal squamous cell cancer (ESCC) based on the coagulation factors. Methods The training cohort of 965 patients with ESCC was retrospectively collected at Sichuan Cancer Hospital from 2012 to 2014, along with clinical characteristics and follow-up information. Risk factors of coagulation status, including 11 blood parameters (platelet [PLT], mean platelet volume [MPV], platelet distribution width [PDW], plateletocrit [PCT], thrombin time [TT], prothrombin time [PT], international normalized ratio [INR], activated partial thromboplastin time [APTT], fibrinogen, D-dimer, and fibrinogen degradation product [FDP]), were studied by least absolute shrinkage and selection operator (LASSO) Cox regression and the Coagulation Index was established. The index was validated in a cohort of 848 patients with ESCC at the same institution, from 2015 to 2016. Results Three variables of PLT, MPV, and fibrinogen were identified by selecting features with coefficients in the LASSO algorithm, and a Coagulation Index was established as follows: Coagulation Index = 0.0005 x PLT (10(9)/L) - 0.0384 x MPV (fL) + 0.1148 x fibrinogen (g/L). A higher Coagulation Index score was significantly associated with higher pT stage and pN stage (p < 0.05). With this prognostic index, patients could be stratified into three risk groups. The 3-year overall survival (OS) rates of the low-, middle- and high-risk groups in the training cohort were 63.5%, 55.5% and 43.1%, respectively (log-rank p < 0.001). Similarly, in the validation set, the respective 3-year OS for each risk group was significantly different across the three risk groups. Multivariate analysis indicated that the Coagulation Index remained a significant factor for predicting OS, independently of pathological TNM stage. Conclusions The Coagulation Index is an independent predictor of survival for patients with ESCC.