private object sync = new object();

        delegate void SetTextCallback(string text);

        private void WorkThread()
        {
            this.ReadText();
            this.WorkThread();//为了循环
        }

        private void ReadText()
        {
            int a;
            lock(sync)
            {
                a = Convert.ToInt32(textBox1.Text);
            }
            Thread.Sleep(1000);
            a++;
            lock(sync)
            {
                this.SetText(a.ToString());
            }
        }

        private void SetText(string text)
        {
            // InvokeRequired required compares the thread ID of the
            // calling thread to the thread ID of the creating thread.
            // If these threads are different, it returns true.
            if (this.textBox1.InvokeRequired)
            {
                SetTextCallback d = new SetTextCallback(SetText);
                this.Invoke(d, new object[] { text });
            }
            else
            {
                this.textBox1.Text = text;
            }
        }

            Thread t = new Thread(new ThreadStart(WorkThread));
            t.Start();