I want to measure 100A AC/DC current.
i found one current sensor.
it will work with arduino nano?
Please help 
It looks like it could work. Do you have the manufacturer, part number, and specs for the PC board assembly? Without the datasheet it's a shot in the dark.
The [u]WCS1500[/u] is only the current sensor module.
i don't have any part number.
"Any current flowing through this hole will generate a magnetic field
which is sensed by the integrated Hall IC and converted into a proportional
voltage. "
This is possible?
The first module you posted has digital out as well as analog and no relay.
More details - DIY BYO Do It Yourself AC DC Hall Effect Current Sensor Transducer – Measure-Current
Don't apply 8 Volts or you can damage your Arduino.
The specs for the WCS1500 (without any additional circuitry) say 11mV per Amp. With the additional unknown circuitry, we don't know.
The Arduino's analog input can read 0-5V with the default 5V reference. The 10-bit analog-to-digital converter reads from 0-1023, so that's about 5mV (0.005V) per count (or ~2.2 counts per amp).