An optical system, comprising: a lens group comprising a third lens, a second lens and a first lens arranged successively along a propagation direction of incident light; the first lens comprises a first surface and a second surface, the second lens comprises a third surface and a fourth surface, the second surface and the third surface are arranged adjacent to each other, and are both Fresnel surfaces, the third lens comprises a fifth surface and a sixth surface, the fifth surface and the fourth surface are arranged adjacent to each other, the first surface is a convex surface, the fourth surface is a convex surface, at least one of the fifth surface and the sixth surface is a concave surface, the optical system has an imaging spot size less than 50μm, and the spot size is all less than two display pixels, the absolute value of the radius R1 of the first surface satisfies 35mm ≤ R1 ≤ 65mm; the absolute value of the radius R2 of the second surface satisfies 20mm ≤ R2 ≤ 40mm, the absolute value of the radius R3 of the third surface satisfies 20mm ≤ R3 ≤ 40mm; the absolute value of the radius R4 of the fourth surface satisfies 30mm ≤ R4 ≤ 60mm, the absolute value of the radius R5 of the fifth surface satisfies R5 ≥ 30mm; the absolute value of R6 of radius on the sixth surface satisfies 30mm ≤ R6 ≤ 60mm, an effective focal length f1 of the first lens is 20mm ≤ f1 ≤ 40mm; an effective focal length f2 of the second lens is 20mm ≤ f2 ≤ 40mm; an effective focal length f3 of the third lens is -75mm ≤ f3 ≤ -35mm, a first spacing is provided between the first lens and the second lens; a second spacing is provided between the third lens and the second lens, and the second spacing is greater than the first spacing, and a third spacing is provided between the third lens and the display screen; and the first lens, the second lens and the third lens are located on a same optical axis, the first spacing T1 is set to 0.2mm ≤ T1 ≤ 1mm, the second spacing T2 is set to 1mm ≤ T2 ≤ 3mm, the third spacing T3 is set to 5mm ≤ T3 ≤ 15mm, the thickness h1 at the center of the first lens is 2mm ≤ h1 ≤ 4mm; the thickness h2 at the center of the second lens is 3mm ≤ h2 ≤ 5mm; the thickness h3 at the center of the third lens is 2mm ≤ h3 ≤ 4mm. a lens group comprising a third lens, a second lens and a first lens arranged successively along a propagation direction of incident light; the first lens comprises a first surface and a second surface, the second lens comprises a third surface and a fourth surface, the second surface and the third surface are arranged adjacent to each other, and are both Fresnel surfaces, the third lens comprises a fifth surface and a sixth surface, the fifth surface and the fourth surface are arranged adjacent to each other, the first surface is a convex surface, the fourth surface is a convex surface, at least one of the fifth surface and the sixth surface is a concave surface, the optical system has an imaging spot size less than 50μm, and the spot size is all less than two display pixels, the absolute value of the radius R1 of the first surface satisfies 35mm ≤ R1 ≤ 65mm; the absolute value of the radius R2 of the second surface satisfies 20mm ≤ R2 ≤ 40mm, the absolute value of the radius R3 of the third surface satisfies 20mm ≤ R3 ≤ 40mm; the absolute value of the radius R4 of the fourth surface satisfies 30mm ≤ R4 ≤ 60mm, the absolute value of the radius R5 of the fifth surface satisfies R5 ≥ 30mm; the absolute value of R6 of radius on the sixth surface satisfies 30mm ≤ R6 ≤ 60mm, an effective focal length f1 of the first lens is 20mm ≤ f1 ≤ 40mm; an effective focal length f2 of the second lens is 20mm ≤ f2 ≤ 40mm; an effective focal length f3 of the third lens is -75mm ≤ f3 ≤ -35mm, a first spacing is provided between the first lens and the second lens; a second spacing is provided between the third lens and the second lens, and the second spacing is greater than the first spacing, and a third spacing is provided between the third lens and the display screen; and the first lens, the second lens and the third lens are located on a same optical axis, the first spacing T1 is set to 0.2mm ≤ T1 ≤ 1mm, the second spacing T2 is set to 1mm ≤ T2 ≤ 3mm, the third spacing T3 is set to 5mm ≤ T3 ≤ 15mm, the thickness h1 at the center of the first lens is 2mm ≤ h1 ≤ 4mm; the thickness h2 at the center of the second lens is 3mm ≤ h2 ≤ 5mm; the thickness h3 at the center of the third lens is 2mm ≤ h3 ≤ 4mm.