The invention provides an N-type solar cell and a preparation method of selective back surface fields of the N-type solar cell. The preparation method of the selective back surface fields of the N-type solar cell comprises the following steps that phosphorus slurry is printed in a preset position of a N-type substrate; high temperature diffusion is conducted on the N-type substrate printed with the phosphorus slurry; phosphorus oxychloride gas is supplied; and the selective back surface fields are formed. A highly-doped region is formed on the N-type substrate printed with the phosphorus slurry; a lowly-doped region is formed on the N-type substrate not printed with the phosphorus slurry by the diffusion of the phosphorus oxychloride gas; in this case, the selective back surface fields with different doping concentrations are formed on the N-type substrate; the preparation of the selective back surface fields can be achieved through a high-temperature process by the method; and damage to the N-type substrate due to high temperature for many times is avoided.