[Background] Phytic acid is an organophosphorus compound which are widespread in plant tissues. It can chelate nutrient elements such as metal ions and protein in plant tissues, making them unable to be absorbed and utilized by herbivorous monogastric animals. The phytase can effectively catalyze the hydrolysis of phytic acid. [Objective] In order to promote the research and industrial application of Debaryomyces castellii phytase, we constructed a recombinant strain that heterologously expressed Debaryomyces castellii phytase in Pichia pastoris. [Methods] The phytase gene from Debaryomyces castellii was optimized and transformed into Pichia pastoris GS115. The high expression strain was obtained by screening copy number, knocking out proteases, and co-expressing molecular chaperones and transporters. [Results] The enzyme activity in the fermentation supernatant of the recombinant strain GS115/DCphy(ΔPep4)(BFR2) is 7 times that of the low-copy strain. [Conclusion] The results can provide some guidance for the heterologous expression and potential industrial application of Debaryomyces castellii phytase.