Abstract: Through comparing the pavilions of Jin and Yuan dynasties, Yingzao fashi and related Sung paintings, the paper summarized the structure practice of four-pillar pavilion in the period from the 10th to the 14th century, which includes how to position purlin, how to determine the length of flying eaves and rafter, how to calculate the length of overhanging purlin, and how to rise the intermediate purlin below. 5 specific conclusions were put forward: 1) the height of the ridge purlin is between a fourth to a half of the distance of rear and front eaves purlin; 2) the modulus of rafter is between 9 to 10; 3) the rules of the length of rafter relate only to large pavilion, using provisions of Yingzao fashi, while to small one, the length is determined by the size of the eaves step frame; 4) the length of overhanging purlin is between four fifths to one of the size of the step frame for pavilion with gable and hip roof; 5)The methods of raising the intermediate purlin below can be classified into three categories:“cantilevered by dougong”, “transition state”, “rised by beam”, each of which can be further subdivided into two approaches. Step further, combed the historical evolution of the methods above. The results can be used to supplement the architectural structure of the middle ancient pavilion，also to supplement Yingzao fashi.