Owning to interactions between phosphorus and aluminium in solution，the key to study effect of phosphorus on aluminum toxicity to plants is to select an appropriate method to treat phosphorus and aluminium. In this study comparison was made between two phosphorus and aluminium treatment methods. Results showed that adoption of the method based on calculation of aluminium activity demonstrated that phosphorus could alleviate aluminium toxicity to wheat，while the application of the P-Al alternate treatment method revealed that phosphorus aggravated aluminium toxicity to wheat. By directly determining concentration of inorganic monomeric aluminium in Al-P treatment solutions，it was found that the toxic aluminium concentrations of treatment solutions decreased with increasing phosphorus supply though the estimated aluminium activities by GEOCHEM were at the same levels，so that the alleviating effect of phosphorus on aluminium toxicity to plants in the calculating method might result from decreasing concentration of toxic aluminium in the solutions. The alternate treatment method can avoid P-Al interaction in the solution，thus can keep phosphorus and aluminium at the same concentration level. Moreover，long-term application of this alternate method may also eliminate the impact of phosphorus and aluminium not being treated at the same time on accuracy of the experiment. Therefore，this alternate method may probably be a relatively workable one. Under P-Al alternate treatment，phosphorus aggravating aluminium toxicity to wheat may be associated with phosphorus stimulating aluminium accumulation at root tips of wheat.