We propose a compact scheme for high-density and high-energy positron generation. In the scheme, the generation, compression and acceleration of positrons are encompassed in a plasma channel irradiated by an ultra intense laser. In about 20 μm, positrons are accelerated with their energy beyond 20 GeV, and are compressed with a maximal density of 4.1nc. The obtained positron beam with a wave-like density profile is accelerated via the direct laser acceleration.