The present invention discloses a method for preparing a barium titanate and barium titanate based powder by an oxalate process. The method is carried out in the following manner: An aqueous mixture solution containing barium chloride and titanium chloride is added into an aqueous oxalic acid solution, so that barium titanyl oxalate would be precipitated. Then the precipitates are aged, washed and filtered. The filtered barium titanyl oxalate precipitates are crushed, and dried. Then a thermal decomposition is carried out to obtain a agglomerated barium titanate powder, and this is crushed again to obtain the final barium titanate powder. In order to obtain barium titanate based powder such as Ba(Ti1nullzZrz)O3, (Ba1nullxCax)(Ti1nullzZrz)O3, and (Ba1nullxnullyCaxSry)(Ti1nullzZrz)O3, the desired elements (Ca, Sr, Zr and so on) are added to barium titanyl oxalate when crushed before thermal decomposition step. After thermal decomposition and crushing, the barium titanate based powder can be obtained.