The diamond back moth, Plutella xylostella (L.), is a major pest of the cruciferous vegetables around the world. Mycoinsecticide is a choice to alternate the high toxic chemical insecticides to control this pest. However, the application of mycoinsecticides was limited for their slower and instable control effects. In order to comprehend the different infection rates of different fungal strains against insect hosts, the strains SB005 of Beauveria bassiana, SM016 of Metarhizium anisopliae and SP020 of Isaria fumosorosea, which respectively had the LT90s (1.0 × 107sporces/mL) 4.5, 6.3 and 6.1 d, were selected to compare their histopathological feature in infecting the larvae of Plutellaxylostella. The results indicated that SM016 and SP020 strains were similar in symptons and infection process. Differently, the strain SB005 had more disease spots on body and could penetrate the cuticle of headcapsule. These probably are the reason for Beauveria bassiana SB005 strain more quickly kill diamond moth.