Using the tadpole improved clover Wilson quark action on coarse anisotropic lattices, the $\pi\pi$ scattering length in the I=2 channel is calculated within quenched approximation. We show that such a calculation is feasible using small lattices on small computers provided that the finite volume and finite lattice spacing errors are under control. Our results are extrapolated towards the chiral, infinite volume and continuum limit. Comparisons of our results with previous lattice results from JLQCD collaboration, the new results from E865 experiment, and the results from Chiral Perturbation Theory are made. Good agreements are found.