1. A method for estimating a fan life, comprising: providing fans to be checked at a number of M, wherein M is a positive integer; setting a working temperature and a test temperature of the fans, wherein the test temperature is greater than the working temperature; setting an acceleration factor, wherein the acceleration factor has a fixed value; keeping the fans in an operating state under the test temperature, and detecting and recording a number of the damaged fans at intervals of a check time, until N damaged fans are detected, wherein N≧3 and N is a positive integer, comprising: (a) continuously supplying a voltage of 5V to the fans for K hours, wherein K is a positive constant; (b) implementing a load test process, for driving the fans in a pulse width modulation (PWM) mode to perform a load cycle greater than 10 times, wherein in each load cycle, the voltage of 5 V is continuously supplied to the fans for a first period, and then the voltage of 5 V is stopped for a second period; (c) checking the fans, and recording the number of the damaged fans and a occurrence time of the damage, wherein the fans are determined to be damaged when at least one condition selected from the group consisting of a first condition and a second condition is satisfied, the first condition is where a starting voltage of one of the fans increases from an initial starting voltage (X) to (X+0.5) volts, and the second condition is where the voltage of 5 V is supplied to the fans and a rotation speed of one of the fan is larger than 1.15 times of an initial rotation speed; and (d) repeating the steps (a) to (c), until N or more damaged fans are detected; simulating a distribution of time points when the fans are damaged with a Weibull distribution model, and calculating a shape parameter (β) and a characteristic life (α) of the Weibull distribution model, wherein the Weibull distribution model is F ⁡ ( t ) = 1 - ⅇ - ( t α ) β and the shape parameter (β) is greater than 1; calculating a life value of the fans at the test temperature by using the shape parameter and the characteristic life; and calculating a life value of the fans at the working temperature by using the acceleration factor.