I create a new form and call from the parent form as follows:
loginForm = new SubLogin();
loginForm.Show();
I need to display the chi
Assuming your code is running inside your parent form, then something like this is probably what you're looking for:
loginForm = new SubLogin();
loginForm.StartPosition = FormStartPosition.CenterParent
loginForm.Show(this);
For the record, there's also a Form.CenterToParent() function, if you need to center it after creation for whatever reason too.