unit Unit1;

uses   
    //...

type   
    Form1: TForm1;

implementation

procedure TForm1.FormCreate(Sender: TObject);
begin
  Form2 := TFrom2.create(self);
end;

procedure TFrom1.Button2Click(Sender: TObject);
begin
    Form1.caption := 'Hi'; //不要再TForm1类中国实用Form1
end;

unit Unit2;

var
    Form2: TForm2;

implementation

//...

unit Unit1;

uses   
    //...

type   
TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
private
    FForm:TForm;
public
    property Form: TType read FForm write FForm;
end;

var
    Form1: TForm1;



implementation

procedure TForm1.FormCreate(Sender: TObject);
begin
  Form2 := TFrom2.create(self);
end;

procedure TFrom1.Button1Click(Sender: TObject);
begin
    if Assigned(FForm) then
        TForm2(FForm).Shoe;//访问的是内部成员FForm,主要FForm需要转型.
end;

procedure TFrom1.Button2Click(Sender: TObject);
begin
   self.caption := 'Hi';//在TForm1类中实用self代替Form1.
end;

//一下是项目文件中的内容
program Project1;
uses
    Forms,
    unit1 in 'Unit1.pas'{Form1},
    Unit2 in 'Unit2.pas'{Form2};

begin
    Application.Initialize;
    Application.CreateForm(TForm1,Form1);
    Application.CreateForm(TForm2,Form2);
    //通过属性传递Form2的引用
    Form1.FForm := Form2;
    Application.Run;
end;