This　study　investigated　the　effective　length　of　the　reader　solenoid　coil　used　for　oil-well　drilling,　and　the　time　required　for　the　communication　between　rapidly　moving　microtags　and　the　reader　solenoid　coil　attached　to　the　equipment　pipeline　was　calculated.　The　effective　length　of　the　solenoid　coil　was　computed　for　both　static　and　moving　microtags.　Then,　a　mathematical　model　was　developed　to　describe　the　relationship　among　the　effective　length　of　the　reader　solenoid　coil,　baud　rate,　number　of　data　bits,　and　microtag　speed.　Calculations　were　performed　to　design　two　reader　solenoid　coils,　which　were　tested　experimentally　with　a　carrier　frequency　of　125　+/-　10　kHz.　The　results　show　that　the　effective　length　of　the　reader　solenoid　coil　is　proportional　to　the　microtag　speed　and　number　of　data　bits　but　inversely　proportional　to　the　baud　rate.　The　proposed　system　provides　a　continuous　energy　supply　to　the　microtags,　and　the　moving　microtag　identification　rate　by　the　reader　is　100%.　The　experimental　and　calculation　results　were　in　good　agreement.　Furthermore,　reader　solenoid　coils　of　two　lengths　were　used　in　the　downholes　of　six　oil-well　drilling　systems　over　two　years.