A parameter adjustment device and method thereof for a stimulator is disclosed. The parameter adjustment device comprises a generation unit, a user interface and a process unit. The generation unit generates a test MAP based on a current MAP. The user interface displays the current MAP and the test MAP for choosing one of them as the preferred MAP, and displays a major and a minor for choosing again, the major and the minor is defined as a significant difference and a little difference between the test MAP and the current MAP respectively. The process unit computes the acceptance probability of the preferred MAP based on a major or minor probability correspondence relationship and determines a next MAP by comparing the acceptance probability with the test probability. When one of the termination conditions is satisfied in an iterative operation, the next MAP is outputted as the best MAP.