In operation of civil aircraft, the maximum takeoff weight is limited by the performmance when one engine fails, and it"s of great significance to optimize takeoff performance by excuting different obstacle clearing methods to increase the maximum takeoff weight. Based on the theoretical analysis of the takeoff flight path defined in the regulations, this paper calculated the maximum takeoff weight corresponding to the standard second segment, extended second segment, and fourth segment obstacle clearing method, and analysed their obstacle clearence, climb gradients, and takeoff distance to ascertain the key factor which limits the maximum takeoff weight. Different distances and gradients are combined to simulate various terrain conditions, and the takeoff weights of standard second segment and forth segment obstacle clearing method in those terrain conditions are calculated. The result shows that using of fourth segment obstacle clearing method can effectively improve the maximum takeoff weight of the aircraft. And the larger the gradient of the obstacle is, the more significant the improvement is. At plateau airports with complex terrain, the use of fourth segment obstacle clearing method can significantly improve takeoff performance and operational efficiency.1\