An LED having an N type AlInGaN contact layer and a preparation method. The structure comprises a substrate, a nucleating layer, a buffer layer, an N type GaN layer, a multi-quantum-well luminous layer and a P type structure in sequence from bottom to top, and the P type structure includes a P type AlGaN layer, a P type GaN layer and an N type AlInGaN contact layer in sequence. The nucleating layer, the buffer layer, the N type GaN layer, the multi-quantum-well luminous layer, the P type AlGaN layer, the P type GaN layer and the N type AlInGaN layer are grown on the substrate in sequence, through regular changes of the doping amount of In in the N type AlInGaN layer arranged in an LED chip, energy band distribution of the N type AlInGaN layer is changed, a blocking effect of a valence band of the N type AlInGaN layer on hole injection is weakened while a blocking effect on electrons is not weakened, surface roughness can be improved to some extent, and ohmic contact of the LED chip can be reduced by about 10%.