The detections of high energy neutrinos from gamma-ray bursts (GRBs) will prove GRBs as the source of high energy cosmic rays. We point out here that based on the relations of electromagnetic radiation and the neutrino flux in the photo-pion production, the observations of GRBs by Fermi satellite has put a constraint on GRB neutrino flux, even more stringent than the constraint by the current IceCube limit. IceCube with 40 string configuration needs at least 400 GRBs to detect one up-going muon neutrino.