We performed systematic investigation of various doping approaches and the effects on superconductivity in the recently-discovered FeAs-based superconductors. Main three type doping approaches are presented as below. (1) Superconductivity induced by Th doping in Ln-1111 system and a record of Tc=56 K is reached in Gd1-xThxFeAsO system. (2) Superconductivity induced by doping of Co or Ni on Fe site in both 1111 and 122 systems. A dome –like doping dependence of Tc is observed. The result points to an itinerant picture of 3d electrons in the iron arsenides. We have also observed that a correlation between Tc and normal state thermopower. (3) The doping effect of non-magnetic impurity Zn is investigated and a possible change in the pairing symmetry with doping level is proposed. (4) Chemical pressure is studied by doping of P on As site and chemical pressure induced superconductivity is observed. In P-doped Eu-122, a coexistence of superconductivity and ferromagnetism is observed. In P-doped Ba-122 system, a possible quantum critical point of Fe SDW is evidenced. A rich phase diagram of CeFeAs1-xPxO system is revealed and we suggested that the inter-layer Kondo coupling plays an important role in the rare earth iron pnictides.