By using the maximum open interest as the standard of judging the main index futures contract, this paper studies the inner regularities between the main index futures contract transference and the price discovery capacity. Based on the VAR model and the VECM model, the lead-lag relationship between the old main contract and the new main contract is studied. And with the PT model and IS model,the price discovery contribution of the old main contract and the new main contract are measured. Thus studies the influence of the main contract transference on the price discovery capacity. This study shows that after the transference, there is a significant reversion in the direction of the lead-lag relationship between the old main contract and the new main contract, and the price discovery capacity of the new main contract is greatly enhanced. Another significant change is the contribution degree of price discovery capacity of the old main contract and the new main contract, which means the new main contract has a greater price discovery contribution.