In this paper a model of slip distribution is proposed for the 1746 Callao earthquake and tsunami based on macroseismic observations written in historical documents. This is done using computational tools such as tsunami numerical simulation through a forward process by trial and error. The idea is to match historical observations with numerical simulation results to obtain a plausible seismic source model. Results show a high asperity from Cañete to Huacho, which would explain the great destruction in this area. The rupture directivity of the seismic source, from north to south, would explain the value of the arrival time of the first tsunami wave at Callao. A kinematic seismic source model was used as a first approximation of the event. The estimated magnitude was Mw9.0.