The lifetime warranty agreement is an independent unnamed contract, and the contract assumption is often too simple in practice with terms deliberately left open. There should be a presumption of establishment of contract based on the spirit of “advocating bargain”, and through the contract interpretation to supplement the loopholes in the contract. In the absence of a clear agreement, the “lifetime” should be determined according to the service life in general of different products in the quality qualified under normal use, and the starting date is the date of purchase.“Warranty” in the absence of clear agreement should be paid in accordance with the market prices, except having already agreed that only need to pay the fee of parts needed for maintenance.