We demonstrate a harmonic mode-locked ytterbium-doped fibre ring laser,which consists of a polarizationsensitive isolator,two polarization controllers,two 976nm laser diodes as the pump source and a two-segment ytterbium-doped fibre.Utilizing an additive pulse mode-locked technique based on nonlinear polarization evolution.the ytterbium-doped fibre laser can operate in mode-locked state bly adjusting the position of polarization controllers.The cavity fundamental repetition rate is 23.78 MHz.We also observe the second-and third- armonic mode locking in the normal dispersion region,and their repetition rates are 47.66MHz and 71.56MHz,respectively.Over-driving of the saturable absorber in the harmonic mode-locking pulse is analysed and discussed in detail.