In this paper we experimentally studied the instabilities of pre-stretched viscoelastic fluid in cross-slot devices. We first investigate the instability of the flow in a standard cross-slot at different Weissenberg numbers without pre-stretch. It is found the viscoelastic flow is transformed from the steady symmetric state to the instabilities states including the steady asymmetric state and the non-periodically oscillated asymmetric state. This is due to the extension of the polymer in the viscoelastic fluid at the stagnation point stretched by the extensional flow in the cross-slot. We then modified the cross-slot channel in which the viscoelastic fluid is pre-stretched before entering the crossroad region. Due to the pre-stretch, elastic energy is pre-stored in the polymer, and the energy required to fully extend the polymer is also different with those extending from equilibrium state. As a result, the flow remains in the steady asymmetric state in all tested Weissenberg number condition.

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