Abstract: The first task of applying deterministic chaos theory to studying the dynamics of fluidized bed from the time series of pressure fluctuation is the computation of delay time of reconstructed phase space. This paper studies the influence of periodic and stochastic signal on the computation. It is suggested that the periodic components that possibly exist in the measured instantaneous pressure could make the delay time correspond to the first minimum of mutual information increase, such as the result of Dow and Halow [6] .A method of extracting periodic tendency term from the instantaneous pressure signal and its statistics test are provided. After removing periodic components from the original signal, the delay time that corresponds to the first minimum of mutual information can be determined correctly.