how to using USB (CY7C68013) with Cyclone III

The CY7C68013A EZ-USB will not connect directly to the Avalon bus, you will need to write a bit of logic to do that. How much work the NIOS core will have to do will depend on how sophisticated that logic is.

As FvM said, it provides a fast FIFO interface so there's not much for NIOS to do in terms setting up the transfer.

However, the EZ-USB buffers can't hold more than 4 packets at a time.

Note that at full speed (12 Mbit/s) each packet can be 512 bytes but at high speed (480 Mbit/s) it's only 64 bytes.

So, a minimal effort solution would require NIOS to read/write data in batches of 4*pktSize or less.

If this is not good enough, you can improve this by making the interface a bit more sophisticated.

You can add some FIFOs of your own to the Avalon/EZ-USB interface to increase the batch size.

Or you can have the Avalon/EZ-USB interface perform DMA transfers directly to the NIOS RAM. In this case, I'd look at EZ-USB's Master mode, I think it should simplify the DMA logic.