The invention provides a display device, a gate driver and a controlling method thereof. The gate driver comprises a plurality of clock signal ends, a noise reduction control end, N stages of cascadedgate driving units and a control unit, wherein each stage of gate driving units in the N stages of cascaded gate driving units is connected with a corresponding clock signal end; the N stages of cascaded gate driving units are also connected with the noise reduction control end; each stage of gate driving units pulls up voltage of an output end of the stage of gate driving unit according to a signal of the corresponding clock signal end, and noise reduction is also carried out according to the signal of the noise reduction control end, wherein N is an integer being more than 1; the control unit is respectively connected with the plurality of clock signal ends and the noise reduction end; the control unit is used for detecting signals of the plurality of clock signal ends and outputting aneffective electrical level to the noise reduction control end when a signal of at least one clock signal end is abnormal so that noise reduction on the N stages of gate driving units is carried out;therefore, multi-output production can be prevented, and the dependability of the gate driver is improved.