The solutions of a family of generalized Kadomtsev-Petviashvili equation in two dimensions, (ut + UmUx ... o .2 = 1. If m _> 4, then the' solution can blow up in finite time. We show that if 1 _< m < 4, ...... /61 = -yuo ~o ~ ( 1/muo + ~ Ouoo + yuoy).