The density of the host larvae - oriental fruit fly affected the parasitic effect of P. incisi significantly, which accorded with the Holling II Equation : Na =0.560 8Nt/( 1 +0.011 89Nt). The more host larvae provided, the more larvae were parasitized, but the increasing extent was getting smaller when the host density was no more than thirty per slice of guava, while the increasing extent was getting much smaller when the host density was more than thirty per slice of guava. What's more, the density of P. incisi also affected the parasitic effect which accorded with Hassell - Varley Equation a = 2: 073Pt-1.8244. The more P. incisi provided, the less larvae were searched by parasitoids because of some interference acts of individuals. Bactrocera dorsalis none