The existing finite element model is suitable only for low frequency range and not precise because to its first order resonant frequency is much lower than that of one-dimension model when its element number is 1 and 2. A modified small element-number finite element model is pressented here, it equates its first order resonant frequency to that of one-dimension model by modifying the shunt admittance of the pipes when the element number n=1 and n=2, therefore increases its usage frequency range and computation precision greatly. Corroboration of our model's modified effectiveness is given by the simulated results of the water hammer of a single pipe after valve closure. When n=2, the calculated results obtained by using the existing finite element model deviate from those obtained by using one-dimension model obviously , but the calculated results by using the modified finite element model agree well with these by using one-dimension model.