How much is the maximum current of FPGA

What is it you are trying to calculate? The spec you are referring to is simply to indicate that the maximum current each I/O pin can source/sink is 20mA. Beyond that you will damage the FPGA. The amount of current actually drawn by the I/O pin depends on what you've got connected to it.

Now if you are trying to figure out how much current your FPGA is going to draw in your design so that you can figure out how much power to provide it, that is a much more complicated issue. Altera provides tools that allow you to estimate the power consumption of your design and figure out how large to make your power supplies.

The best one is the PowerPlay power estimator built into the Quartus II software.

Jake