An optical lens for lighting fixture includes a body, which comprises a bottom surface and a light-exit surface at opposing bottom and top sides thereof, an elongated groove formed in the bottom surface, a light incident surface, a first intersection line and a second intersection line respectively connected between the two ends of the elongated groove and the bottom surface, a first line segment and a second line segment respectively connected between the light incident surface and the bottom surface, a first virtual line defined between the two ends of the first line segment, a first distance that is the shortest distance between the two ends of the first intersection line, and a SAGi that is the shortest distance between any point at the first line segment and the first virtual line and satisfies the equation: 0≦|SAGi/first distance|×100≦2.8.