RSSi value is Zero

Am using estimote beacon when i scan the beacon some time i got rssi value is 0. how to solve this and why its happens.

This usually means that the iOS device hasn’t recently detected the beacon, so it doesn’t know what the RSSI is. After a short while (a few seconds usually), if it continues not detecting the beacon, it’ll drop from the ranging list completely.

You can lower the advertising interval, up the Tx Power, and ensure clear line-of-sight to the beacon, in order to minimize this happening.