An optical element, comprising: a rectangular light guide plate, comprising a front surface for outgoing light, a bottom surface opposite to the front surface for guiding light, a first side surface for receiving light and a second side surface opposite to the first side surface; a light source setting portion, located on the outer side of the bottom surface near the first side surface and provided with a central axis where a light source is set, wherein a light emitting direction of the light source faces away from the rectangular light guide plate; a parallel light lens group configured to adjust light of the light source to be parallel light and a total reflection lens group, disposed between the parallel light lens group and the first side surface; characterized in that the parallel light lens group is disposed at a side of the light source setting portion near the rectangular light guide plate; and in that the total reflection lens group comprises a first total reflection surface, disposed on a side of the parallel light lens group away from the light source and totally reflecting the parallel light from the parallel light lens group, a second total reflection surface, disposed on a side of the first total reflection surface near the rectangular light guide plate, and a third total reflection surface, disposed opposite to the second total reflection surface, wherein the first and second total reflection surfaces are arranged such that a part of the parallel light from the parallel light lens group is subjected to total reflection only twice, namely first at the first total reflection surface and then at the second total reflection surface to form a first parallel light parallel to the front surface, and the first parallel light enters the first side surface to make the second side surface emit light; and wherein the first, second and third total reflection surfaces are arranged such that another part of the parallel light from the parallel light lens group is subjected to total reflection only three times, namely first at the first total reflection surface, then at the second total reflection surface and then at the third total reflection surface to form a second parallel light oblique to the front surface, and the second parallel light enters the first side surface to make the front surface emit light. a rectangular light guide plate, comprising a front surface for outgoing light, a bottom surface opposite to the front surface for guiding light, a first side surface for receiving light and a second side surface opposite to the first side surface; a light source setting portion, located on the outer side of the bottom surface near the first side surface and provided with a central axis where a light source is set, wherein a light emitting direction of the light source faces away from the rectangular light guide plate; a parallel light lens group configured to adjust light of the light source to be parallel light and a total reflection lens group, disposed between the parallel light lens group and the first side surface; characterized in that the parallel light lens group is disposed at a side of the light source setting portion near the rectangular light guide plate; and in that the total reflection lens group comprises a first total reflection surface, disposed on a side of the parallel light lens group away from the light source and totally reflecting the parallel light from the parallel light lens group, a second total reflection surface, disposed on a side of the first total reflection surface near the rectangular light guide plate, and a third total reflection surface, disposed opposite to the second total reflection surface, wherein the first and second total reflection surfaces are arranged such that a part of the parallel light from the parallel light lens group is subjected to total reflection only twice, namely first at the first total reflection surface and then at the second total reflection surface to form a first parallel light parallel to the front surface, and the first parallel light enters the first side surface to make the second side surface emit light; and wherein the first, second and third total reflection surfaces are arranged such that another part of the parallel light from the parallel light lens group is subjected to total reflection only three times, namely first at the first total reflection surface, then at the second total reflection surface and then at the third total reflection surface to form a second parallel light oblique to the front surface, and the second parallel light enters the first side surface to make the front surface emit light.