Abstract: Based on FGGE Ⅲb data of 1979, a study was done of the structure of the circulation and temperature field with quasi-40 day periodic oscillation (QDPO) in the cross-sections along 15° N and Equator over 30°-150° W, and a discussion of their changes and relation to the active and the break monsoon over Asia is also presented. The results are as follows:1)The updrafts within monsoon trough over Asia not only form the strong meridional circulation cell, but also East-West(an anomaly from zonal mean) circulation cells with different thermodynamic structure over both sides of the trough, which may be significantly affected by QDPO.2) At 15 °N the downdrafts(updrafts) covering north Africa and Saudi Arabia west of about 60 °E intensify as they extend eastward to the South China Sea-the Philippines around 130 °E, then cause downward (upward) transport of easterly (westerly) momentum in the upper(lower) air east(west)of it, which leads to break (active)monsoon with interaction beteen the lower(upper)-level westerly(easterly) west(east)of 130 °E. The eastward propagating positive (negative) temperature perturbations are associated with strong upward(downward)-motions, implying that this region is a kinetic energy source for QDPO.3)On the equatorial cross-section, the wind perturbations propagate eastward and upward with westerly momentum transporting downward, while the kinetic energy for quasi-40 day periodic perturbations were converted into potential energy, which means that the perturbations are significantly different from Kelvin wave in dynamic properties.