The invention relates to the technical field of image processing, and provides an IOS image loading performance optimization method in order to solve the technical problems of unsmooth rendering display and insufficient memory in the image loading process, which comprises the following steps of: 1, loading data held by a bitmap; step 2, generating a thumbnail; 3, allocating a memory cache region to manage decoding operation, reading the thumbnail from a disk to a memory, decoding thumbnail data in the memory, and setting the thumbnail data as a bitmap thumbnail; step 4, packaging the bitmap thumbnail into a picture object, wherein the picture object holds data reference; and step 5, directly using bitmap thumbnail data held by the picture object by the picture layer. By adopting the mode, the problems of jamming and flash back of the application are prevented, and the condition of insufficient memory is effectively avoided.