The invention provides a forming process of anode foils for extra-high voltage aluminium electrolytic capacitors, comprising the following steps: placing aluminium foils which undergo electrolytic corrosion in pure water at 90 DEG C or above to carry out pretreatment; then carrying out first-stage formation on the pretreated aluminium foils in aqueous solution containing 1-9wt% of boric acid and 0.01-0.6wt% of ammonium adipate; then treating the foils which undergo first-stage formation with phosphoric acid solution at the concentration of 1-10wt%; then treating the foils which undergo phosphoric acid treatment at high temperature; then carrying out second-stage formation on the foils which undergo high temperature treatment in the aqueous solution containing 2-10wt% of boric acid and 0.01-0.09wt% of ammonium pentaborate; then treating the foils which undergo second-stage formation in the phosphoric acid solution at the concentration of 1-10wt%; then treating the foils which undergo phosphoric acid treatment at high temperature; finally carrying out third-stage formation on the foils which undergo high temperature treatment in the mixed aqueous solution containing 2-10wt% of boric acid and 0.01-0.09wt% of ammonium pentaborate and carrying out post-treatment on the foils which undergo third-stage formation in the aqueous solution containing 1-13wt% of phosphoric acid and 0.1-6wt% of ammonia, and cleaning and then drying the foils which undergo post-treatment.