A trim command processing method, a memory control circuit unit, and a memory storage apparatus are provided. The method includes: receiving a trim command from a host system, where the trim command is configured to indicate data stored in at least one logical address among a plurality of logical addresses can be erased; calculating a first data volume of data required to be programmed when a data trim operation is performed according to the trim command; and determining whether to perform a first trim operation or a second trim operation according to the first data volume.