Abstract: Design train of thought and principles is brought out based on analysis on noise source and characteristics in rapier loom’s tension control. For low pass filter bring lag phase and increase time constant of generalized plant，the influence of filter on design controller is analysis based on definition of difficult control degree and controller design method on rapier loom’s tension is brought out. Results of matlab’s simulink simulation show effectiveness of analysis and design method on filter. That is used as a basis of design on actual rapier loom’s tension control filter and controller

Key words: filter, warp tension control, rapier loom, difficult control degree