A display device and a display panel thereof, and an OLED display device are provided. The OLED display device includes: a red light-emitting structure, a green light-emitting structure, and a blue light-emitting structure, where (n3z-n3xy)-(n1z-n1xy)≥a first preset value, and (n3z-n3xy)-(n2z-n2xy)≥a second preset value, where ranges of both the first preset value and the second preset value are 0.1˜0.3; n1z is a sum of refractive indexes of respective layers of the red light-emitting structure in a thickness direction; n1xy is a sum of refractive indexes of the respective layers of the red light-emitting structure in a vertical thickness direction; n2z is a sum of refractive indexes of respective layers of the green light-emitting structure in the thickness direction; n2xy is a sum of refractive indexes of the respective layers of the green light-emitting structure in the vertical thickness direction; n3z is a sum of refractive indexes of respective layers of the blue light-emitting structure in the thickness direction; and n3xy is a sum of refractive indexes of the respective layers of the blue light-emitting structure in the vertical thickness direction. According to embodiments of the present disclosure, a reflectance of an interface between the blue light-emitting structure and outside at a large angle of view can be reduced, a light transmittance can be increased, a brightness can be enhanced, and further a color shift can be improved.