The invention provides an installing and fixing device for automobile and motorcycle license plates. The installing and fixing device comprises a bumper, an I-shaped support is arranged on the back face of the bumper and comprises two vertical supports and one transverse support, the two vertical supports are fixedly connected through the transverse support, and the upper and lower ends of the twovertical supports are fixedly connected with the bottom ends of four insertion rods; and a clamping plate is arranged on the front face of the bumper, four fixing holes are formed in the periphery ofthe clamping plate in a penetrating manner, the clamping plate is arranged on the four insertion rods of the I-shaped support in a sleeving manner through the four fixing holes, fastening nuts are inthreaded connection to the insertion rods, and the license plates are arranged on the outer sides of the fastening nuts. According to the device, when the license plates are installed, after the bumper is clamped into an arch groove, the insertion rods are sleeved with gaskets, the clamping plate is installed on the insertion rods in a sleeving manner through the fixing holes and is fixed throughthe fastening nuts, an installing base of the license plates is more stable, the license plates are installed on the insertion rods through preserved holes, and finally the license plates are fixed through fastening pieces.