Bone grafting is a good alternative for filling the inevitable void that is created following opening-wedge high tibial osteotomy (OWHTO). This systematic review and meta-analysis evaluated whether bone grafting is necessary for OWHTO and the successful outcomes of OWHTO using either autograft (AU) or allograft (AL). All analyzed studies were acquired from PubMed, Medline, Embase, CNKI, Google Scholar, and Cochrane Library. Data were independently extracted by two coauthors and were analyzed using RevMan5.3. Mean differences, odds ratios, and 95% confidence intervals were calculated. Cochrane Collaboration's Risk of Bias Tool and Newcastle-Ottawa Scale were used to assess the risk of bias. In total, 10 studies were assessed including three randomized controlled trials and seven observational studies. The methodological quality of the trials ranged from low to high. The overall estimate demonstrated that the difference between OWHTO using AU and AL groups and OWHTO using no filling group was not statistically significant for the loss of correction, and complications, but OWHTO using no filling group statistically showed better knee society score. Pooled results of reoperations, lateral cortex breaches, complications, and clinical function assessments showed no significant difference between AU and AL materials. Using AL statistically reduced the operative time compared with using AU. OWHTO with or without bone graft does not affect postoperative complications. No loss of correction was observed due to the lack of bone grafting. In addition, OWHTO without bone graft performs better for postoperative clinical function assessment. Complications and clinical results of medial OWHTO were similar using AL and AU and neither reported a median loss of correction of following OWHTO. Compared with using AU, using AL avoids harvest site complications and reduces operative time. To sum up, OWHTO without any bone graft is recommended for medial unicompartmental osteoarthritis of the knee. Further large-sample, multicenter, high-quality, randomized controlled trials are warranted to verify the outcomes of this meta-analysis.