The interference patte of two Bose-Einstein condensates released from a double-well potential for different holding times is theoretically investigated using a decoupled two-mode Bose-Hubbard model.For two coherently separated condensates,the interference displays a periodic behavior,which is closely related to the atomic inter-action.A remarkable parity effect is found in the interference pattes.For certain holding times,the even/odd total number of atoms would result in different interference fringes.The influences of different initial conditions on the evolution of interference and the observation of parity effects are discussed.