Helicon wave plasma has advantages of high couple efficiency,high density,low magnetic field.However,helicon plasma still meets challenges in applications to actual material synthesis,and modification because of unclear couple mechanism and discontinued mode transition[1].In this paper we focus on wave mode diagnostic by B-dot probe.We intend to investigate the couple and propagating of helicon wave in plasma.The reactor,used for experiment,consists of a 16 cm double-saddle antenna surrounding the Pyrex tube,8cm for outer diameter,and a solenoid coils producing an uniform magnetic field in the antenna region.We found that the helicon wave behaves more like a standing wave under the antenna bounded by nearly one wavelength long Pyrex tube resonantly coupled to plasma;while in a longer tube it propagates from antenna and transfers energy far away as shown in Fig.1.