In　traditional　controlled-source　audio-frequency　magnetotellurics　(CSAMT),　the　orthogonal　magnetic　and　electric　field　components　in　the　far-field　region　are　recorded　to　calculate　the　apparent　resistivity.　However,　as　the　distance　between　the　receiver　and　the　transmitter　increases,　the　electromagnetic　signal　weakens　considerably.　Moreover,　as　the　location　of　the　transmitter　is　fixed,　the　location　of　the　far-field　region　also　is　fixed,　which　limits　the　exploration　range.　In　this　study,　a　novel　phased-array　transmitting　source　was　proposed　to　overcome　this　limitation.　In　traditional　CSAMT,　a　grounded　single-dipole　long-line　source　is　used　to　transmit　the　electromagnetic　wave.　This　source　has　a　low　gain　and　no　directionality,　resulting　in　a　low　signal-to-noise　ratio　(SNR)　in　the　area　of　interest　(AoI).　Conversely,　by　using　a　phased-array　source,　beam　control　and　stable　directional　radiation　will　be　achieved　so　that　the　electromagnetic　energy　should　be　capable　of　effectively　focusing　within　the　AoI.　Without　increasing　the　transmitting　power,　the　SNR　should　be　conveniently　enhanced　and　the　size　of　the　AoI　can　be　greatly　increased.　In　this　paper,　the　characteristics　of　the　radiation　field　of　a　single-dipole　long-line　source　and　its　application　in　traditional　CSAMT　are　analyzed.　The　design　principle　and　the　method　of　implementation　of　a　novel　phased-array　source　are　provided.　The　feasibility　and　effectiveness　of　the　proposed　source　are　verified　by　simulations　and　experiments,　and　a　prototype　is　realized.　©　The　Author(s)　2022.