1. A method for determining variable dependency, comprising: A. determining initial variable dependency among variables arbitrarily; selecting partial variables from the variables, and deleting superior variables of the partial variables from a recent variable dependency; B. selecting a legitimate superior variable set from all variables for each of the partial variables respectively with records of the variables, and obtaining a new variable dependency; judging whether to accept the new variable dependency; if the new variable dependency is acceptable, storing the new variable dependency and performing Step C; otherwise, performing Step C directly; and C. judging whether a criterion for stopping a loop is met; if the criterion is met, determining an optimal variable dependency from all of the stored variable dependencies; otherwise returning to Step A to select partial variables.