Objective: To compare the effectiveness of the single plate and combined double plate in the treatment of middle and distal humeral shaft fractures. Methods: Forty-nine patients with middle and distal humeral shaft fractures were treated with single or combined double plates and followed. There were 27 male and 22 female patients, aged from 22 to 76 (44.47±15.53) years old, 12 cases of type A, 22 cases of type B and 15 cases of type C. There were 21 cases in the single plate group, including 12 males, 9 females, 6 cases of type A, 9 cases of type B and 6 cases of type C. There were 28 cases in the combined double plate group, including 17 males, 11 females, 9 cases of type A, 10 cases of type B and 9 cases of type C. A retrospective study was performed to compare the outcomes of two methods regarding operation time, perioperative blood loss, fracture healing time, complications and Mayo Elbow Performance Score (MEPS). Results: Forty-nine patients were followed with 12–18 months. The number of internal fixation failure and Mayo elbow performance score had significant differences between the two groups (P<0.05). However, perioperative blood loss, the operative time, the fracture healing time and number of radial nerve injury had no significant differences (P>0.05). Conclusion: In treatment of the middle and distal humeral shaft fractures, the combined double plate fixation has better affected limb function and more remarkable the operation effect than the single plate fixation.