Prostate cancer (PC) is the second most common diagnosed malignant disease. Long non-coding RNAs (lncRNAs), which account for approximately 98% of the human genome, are becoming increasingly interesting with regard to various diseases and have great potential for diagnosis and prognostic monitoring of PC. To identify a new diagnosis marker for metastatic PC, we enrolled a total of 144 patients with PC, including 57 metastatic and 87 localized PC patients, and 148 healthy subjects. Patients were followed up routinely at 3-month intervals for 5 years. The expression of 10 selected lncRNAs in peripheral blood from participants was measured. Among the 10 selected lncRNAs, the expression of PCGEM1 in the metastatic group was 2.57 times that in the localized group (p < 0.001) and 2.96 times that in the control group (p < 0.001). Patients with higher AJCC stage had significantly elevated PCGEM1 expression (one-way ANOVA, p < 0.001). The relative expression of PCGEM1 in patients with higher Gleason score was also higher than that in patients with lower Gleason score (p = 0.003). Moreover, patients with more than 5 years survival time had significantly lower PCGEM1 expression than the rest (p = 0.017) and patients with elevated PCGEM1 relative expression had significantly shorter survival time (p < 0.001). The present study suggested that PCGEM1 expression in peripheral blood could act as a diagnostic marker of metastatic PC. It would also be a prognostic marker to predict the survival time.