Ma, H.Z. Cao, J.S. Sui, Y.F. Ye, Q. JACoW Geneva, Switzerland 978-3-95450-176-2 10.18429/JACoW-IBIC2015-TUPB028 English 390-392 TUPB028 linac status detector electronics beam-transport Contribution to a conference proceedings 2016 2016-01 http://dx.doi.org/10.18429/JACoW-IBIC2015-TUPB028 http://accelconf.web.cern.ch/AccelConf/IBIC2015/papers/tupb028.pdf The paper will introduce the status for BPMs in the first stage of commissioning at CADS (China Accelerator Driven Subcritical System) Injector I. The measurement principles and results of BPM at injector I are presented. The measurement of BPM is rigorous in the first medium energy beam transport line of CADS Injector I. To ensure the safety of test cryomodule, beam orbit should be corrected to the minimized region. The third order fitting way is used to calculate the position of beam for BPM non-linearity. And the average of data in the single pass window should improve the resolution. Then BBA of BPM can help tracking beam position accurately. Finally the interlock circuit of BPM is tested with the beam.