Prognostic factors of synchronous bone metastatic colorectal cancer (CRC) are still undetermined. We aimed to investigate survival outcome and prognostic factors of patients with synchronous bone metastatic CRC. Information of patients with synchronous bone metastatic CRC were obtained from the Surveillance, Epidemiology, and End Results (SEER) and West China Hospital (WCH) databases. Cases from SEER database composed construction cohort, while cases from WCH database were used as validation cohort. A novel nomogram was constructed to predict individual survival probability based on Cox regression model. The performance of the nomogram was internally and externally validated using calibration curves and concordance index (C-index). Three hundred and eighty-one patients from SEER database were eligible. The median disease specific OS was 9.0 months (95% confidence interval [CI]: 7.3-10.7 months). Multivariate Cox analysis identified seven independent prognostic factors including histological type, differentiation grade, T stage of primary tumor, CEA level, systemic chemotherapy, combined with liver metastasis and combined with lung metastasis. A novel nomogram was established based on these variables. In the internal validation, the C-index (0.72, 95% CI 0.69-0.75) and calibration curve indicated well performance of this nomogram at predicting survival outcome in bone metastatic CRC. In the external validation, the C-index was 0.57 (95% CI 0.46-0.68). The prognosis of synchronous bone metastatic CRC is very poor. Histological type, differentiation grade, T stage of primary tumor, CEA level, systemic chemotherapy, combined with liver metastasis and combined with lung metastasis are independent prognostic factors. Further study is warranted to confirm the practicality of the prognostic nomogram.