By using trapdoor functions with preimage sampling, lattice's growth, and lattice basis randomization in the bonsai tree, a lattice-based proxy signature scheme was proposed.The security of the proxy signature is based on the hardness of average-case SIS (Small Integer Solution) and ISIS (Inhomogeneous Small Integer Solution).It is also existential unforgeability under adaptive chosen-message attack in the random oracle.Compared with the schemes based on factoring or discrete log, the public and secret keys of our scheme are larger, but it requires only linear operation on small integers.