Abstract: A 3D dosimetry system of proton therapy facility was designed and constructed in Institute of Modern Physics. It is composed of 2D profile detector, depth-dose detector and rang tuning detector. Under the 2D detector operating gas C_(3)F_(8) with the pressure of 700 Pa and the anode voltage of +700 V, the position resolution of about (0.54) mm(FWHM) is achieved for 3-components α particles.