Hi
I finnaly understood that the local variable is changed to zero and didn't stay at zero (which means that it doesn't succcefuly read the SBUF???).
here are all my init values.

TMOD = 0x20;
TH1 = 0xFB; // baud ~19200;
TR1 = 1;
SCON = 0x50;
IE=0x90;
EA = 1;
ES = 1;
REN = 1;
RI = 0;

void SerialPort(void) interrupt 4 using 2
{
while(!RI)
{
if(ArrLenFlag==0)
{
ArrLen = _getkey ();
ArrLenFlag = 1;
}
else
{
if(_getkey()=='S')
{
Start_bit = 1;
SaveData(1000);
SaveData(1000);
}
else
{
chr = _getkey ();
SaveData(chr);
}
}
RI = 0;
TI = 0;
}
}

Thank you all for your help.