Active is the reader and tag both have power, read and write distance;
Passive is only the reader has power, the tag has no power, due to the tag needs to take power from the reader's RF field, so read and write the distance is closer.
Active RFID, tags are self-battery, tags can be self-activated, without the reader end, so the reading distance is relatively far. Generally 2.4G band.
Passive RFID, the tag is not with the battery, so you need to read and write the RF signal energy sent over to activate the tag in order to carry out a variety of operations, so the reading distance is generally closer.