The present invention discloses an apparatus of LED flat light signal display, which comprises at least one light emitting diode, a plurality of flat microlens and at least one microlens set. The light emitting diode acts as a light source for discharging light. The flat microlens comprises a plurality of concentric serrated rings for collimating and converging convergence received from the light source. The microlens set comprises at least one microlens unit with a specific geometric shape for receiving light transmitted from the flat microlens to produce a light spot identical to the specific geometric shape, and the micro unit has a lateral side on its external edge to be disposed next to another lateral side of another micro unit to define a geometric plane. The present invention can provide a maximum viewing area with a minimum quantity of LEDs while being applied in dot matrix LED signals or imaging devices, and also make the images produced by the device smoother to enhance the comfort of viewing.