A DNA sequence encoding Der p2 protein having a particular base sequence is codon-optimized for the Pichia pastoris expression system, which is conducive to expressing Der p2 in Pichia pastoris. After gene optimization and adding an activating element to increase the expression of Der p2 in molecular level, it was found that Der p2 is expressed at a higher level as compared with the prior art and has biological activity similar to the natural protein.