The appropriate timing of radiotherapy (RT) for patients after radical prostatectomy (RP) with adverse pathological features (APFs) remains controversial. This systematic review was conducted to compare the efficacy of adjuvant radiotherapy (ART) and salvage radiotherapy (SRT). PubMed, EMBASE, Web of Science and the Cochrane Library electronic databases were searched to retrieve the required. The hazard ratio (HR) and corresponding 95% confidence interval (CI) of overall survival (OS), biochemical recurrence-free survival (BRFS) and distant metastases-free survival (DMFS) were extracted. The survival benefits of ART with SRT (including early salvage radiotherapy (ESRT)) were analyzed. The process of the meta-analysis was performed with RevMan version 5.3. A total of fifteen retrospective studies were finally included in the final analysis including 5586 patients. The pooled analysis indicated that ART could achieve better control of prostate cancer and improve OS (p = 0.0006), BRFS (p < 0.0001) and DMFS (p < 0.0001), when compared to SRT. The subgroup analysis of the 5-year OS rate demonstrated that the ART group still had survival advantages compared to the SRT group (p = 0.0006). However, ART and SRT were comparable in 10-year OS rate (p = 0.07). ART had advantages over SRT in both 5-year (p = 0.0003) and 10-year BRFS (p = 0.0003). The subgroup analysis with different follow-up starting points from RP or RT was essentially consistent with the above results. The pooled analysis also showed that ART was superior to ESRT on OS (p = 0.008) and DMFS (p = 0.03), and comparable to ESRT on BRFS (p = 0.1). According to this meta-analysis, ART could be served as a preferential treatment for patients with APFs after RP to improve prognosis. Certainly, high-quality, multicenter randomized controlled trials (RCTs) are expecting to confirm the outcomes of our meta-analysis in the future.