There are several connections missing or not clear in your schematic. I suggest you go to any of the data sheets that are available. The data sheets will also give the equation for pulse width using a monostable configuration.
i built the circuit , with R1 = 68K and R2 = 39K C = 0.1 micro
but when i test it , the output pin3 indicate 4.5 volts all the time , i thought it'll flash the volt from 0 to 5 ,
i know i'm wrong , may be the frequncy is so hight , tell me plz
Didn't you do the simple arithmatic that is shown in the datasheet for a 555??
The capacitor charges for 7.4 thousandths of a second and it discharges for 2.7 thousandths of a second. Each cycle takes 10.1 thousandths of a second which is a frequency of 99Hz. It is much too fast to see flashing and it is too fast for your voltmeter.
Replace the 0.1uF capacitor with a 10uF capacitor (use the correct polarity) and the output will make about one pulse per second.
The output of an ordinary 555 goes high to 1.4V less than the positive supply voltage if it does not have a high load current. So if your supply is only 5V then the output goes high to 3.6V. It is shown on the datasheet.