What will happen if DO pin is short to ground?

If One pin is set as DO, and voltage is set as high. What will happen if this DO pin is short to ground? What kind of calculation is it on this DO pin?

Good chance that you will blow up the pin because you short it. Same a shorting the power in your house and the fuse trips.

Now in the house, you can reset the fuse (or replace it); in the microcontroller in the Arduino, you can't.

Read the datasheet; safe maximum of a pin is 20mA.

If one pin is set DO?

You mean, if one pin is set OUTPUT? Trying to drive an output pin high while it's shorted to ground is not good, as enough current will flow that it will exceed the maximum rated output current per pin. That said at least for brief shorts, the pin will typically survive; accidental shorts of an output pin to ground aren't an unusual occurence when wiring something up on the bench, it's certainly happened to me plenty of times (whether from jumper wires touching or a solder bridge I hadn't seen), and I can't recall it ever having blown a pin (the only times I've blown a pin have been from a voltage above Vcc touching the pin). So while you should try to avoid accidentally shorting an output to Gnd or Vcc, you should not assume the chip was damaged (though neither should you be surprised if it turns out to have been damaged).

DO means digital ouput, thanks for your answer. I have one more question, one pin is set as DI ( Digital Input), at the beginning Pin Voltage is set as high, what will happen if this pin is short to ground?

Setting an input pin high enables the internal pull-up resistor. Shorting to ground will be safe.