i want to set the decimal value of the dimension to 2 value what is the step to do so..
If you want to set the whole Part or a Drawing decimal value you can look at the bottom right of the screen when you have the model open & select Edit in the measurements area next to the green question mark. Or you can adjust them in the left menu under tolerance\precision when you have the dimension selected, if you just want to adjust that one measurement. If your using millimeters it's usually set to 2 decimal points anyway.
Options - document properties - units - then use the drop down to select how many decimal places.