A memory device includes: a memory array used for implementing neural networks (NN), the NN including a plurality of layers; and a controller coupled to the memory array, the controller being configured for: determining a computation duration of a first data of a first layer of the plurality of layers; selecting a first program operation if the computation duration of the first data of the first layer is shorter than a threshold; and selecting a second program operation if the computation duration of the first data of the first layer is longer than the threshold, wherein the second program operation has a longer program pulse time than the first program operation.