The present disclosure provide a transform method in picture block encoding, an inverse transform method in picture block decoding, and an apparatus. The inverse transform method includes: determining, in a target transform set, a corresponding transform pair of each region of at least two regions that constitute a to-be-decoded current block; inverse transforming each region based on the corresponding transform pair of each region to obtain an inverse transform result of each region; and obtaining an inverse transform result of the current block based on the inverse transform result of each region and a position of each region in the current block, where the at least two regions do not overlap each other, the target transform set includes a correspondence between a transform pair and a position of a region in the current block, and the transform pair includes a horizontal transform core and a vertical transform core.