We report a double pulse electrochemical method to controllably prepare silver nanocrystals (AgNCs) on graphene thin film electrode for fabricating a high performance H2O2 biosensor. The approach relies on two potential pulses that can independently control the nucleation and subsequent growth processes of AgNCs on graphene substrate. This method also allows the observation of AgNCs growing from a particle shape to a nanoplate form by increasing the growth time with the maximum lateral scale up to micrometer scale range. A proposed mechanism for these silver nanoplates (AgNPLs) formation was the oriented growth of small AgNCs and two-dimensional graphene template inducing effect. Such obtained graphene-AgNPLs hybrid thin films exhibit remarkable electrocatalytical activity toward H2O2 electrochemical reduction. Further fabricated nonenzymatic H2O2 biosensor displays a fast amperometric response time of less than 2s and a good linear range from 2 x 10(-5) M to 1 x 10(-2) M with an estimated detection limit of 3 x 10(-6) M. This biosensor also exhibits good stability (RSD, 13%), and high sensitivity of 183.5 mu A cm(-2) mM(-1) as well as high selectivity. The results show that this powerful double pulse potential electrochemical method could enable new opportunities in controllable preparation of multifarious nanomaterials on graphene substrate for their future applications. (C) 2012 Elsevier Ltd. All rights reserved.