在当前页面加入下面方法

- (void)viewWillAppear:(BOOL)animated{

    [super viewWillAppear:animated];

    [self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];

    //去掉导航栏底部的黑线

    self.navigationController.navigationBar.shadowImage = [UIImage new];

}

如果仅设置当前页导航透明，需加入下面方法

- (void)viewWillDisappear:(BOOL)animated{

    [super viewWillDisappear:animated];

    [self.navigationController.navigationBar setBackgroundImage:nil forBarMetrics:UIBarMetricsDefault];

    [self.navigationController.navigationBar setShadowImage:nil];

}