This　letter　proposes　an　efficient　parameterization　of　the　three-dimensional　room　transfer　function　(RTF)　which　is　robust　for　the　position　variations　of　source　and　receiver　in　respective　horizontal　planes.　Based　on　azimuth　harmonic　analysis,　the　proposed　method　exploits　the　underlying　properties　of　the　associated　Legendre　functions　to　remove　a　portion　of　the　spherical　harmonic　coefficients　of　RTF　which　have　no　contribution　in　the　horizontal　plane.　This　reduction　leads　to　a　flexible　measuring-point　structure　consisting　of　practical　concentric　circular　arrays　to　extract　horizontal　plane　RTF　coefficients.　The　accuracy　of　the　above　parameterization　is　verified　through　numerical　simulations.　(C)　2015　Acoustical　Society　of　America