Abstract: Abstract: The amino acid content and the composition of pitaya fruit and 9 kinds of common tropical and subtropical fruits were analyzed in this paper. The result indicated：Pitaya fruit included 17 kinds of amino acids and species are complete. The amino acids total quantities rank fourth, the human essential amino acid content rank second and the children essential amino acid content rank fourth. Pitaya fruit E/T value was 35.07%, the E/N value was 0.54, basically conformed to the requirement of ideal protein. The percentage of each kind of human essential amino acid content in pitaya fruit to the amino acid total quantity and the content of Ile, Leu, Met+Cys, Phe+Tyr, Thr and Val amino acid content were in accord with the pattern spectrum which FAO/WHO revised in 1973, only Lys was moderately lacked．In pitaya fruit, the delicate taste class，the aromatic and the sweet taste class amino acid contents rank sixth，second and second.