使用NSDictionaty来设置文本的属性：
NSDictionary * attributes = @{NSFontAttributeName: [UIFont fontWithName:@"Heiti SC" size:20]};
[confirmBarButton setTitleTextAttributes:attributes forState:UIControlStateNormal];
完整代码：
self.inputToolbar = [[UIToolbar alloc]initWithFrame:CGRectMake(0, 0, 320, 50)];
self.inputToolbar.translucent = NO;
self.inputToolbar.barTintColor= [UIColor colorWithRed:26.0/255.0 green:194.0/255.0 blue:97.0/255.0 alpha:1];
self.inputToolbar.tintColor = [UIColor whiteColor];
UIBarButtonItem *confirmBarButton = [[UIBarButtonItem alloc] initWithTitle:@"Confirm" style:UIBarButtonItemStylePlain target:self action:@selector(doneKeyboard)];
NSDictionary * attributes = @{NSFontAttributeName: [UIFont fontWithName:@"Heiti SC" size:20]};
[confirmBarButton setTitleTextAttributes:attributes forState:UIControlStateNormal];
UIBarButtonItem *spaceBarButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:self action:@selector(doneKeyboard)];
self.inputToolbar.items = [NSArray arrayWithObjects: spaceBarButton, confirmBarButton, spaceBarButton, nil];
self.textView.inputAccessoryView = self.inputToolbar;
参考链接：http://*.com/questions/2720733/how-do-you-set-the-font-size-on-a-uibarbuttonitem