Central Sichuan and south Suining areas

with quite flat structures

rare faults and superficial structures formed once by stress

are ideal regions for trend-surface analysis.Taking seismic structural maps corrected by drilling data as the basis

11 trend-surface equations and 41 maps are obtained by methods of gridded points and adding more well sites and abnormal points. After proper test and under 1% level of significance

quadratic equation has made more achievements than linear equation

and cubic equation even more than quadratic

showing remarkable fitting results.The linear trend surfaces in central Sichuan not only reflect regional dipping but also the old Indo-Sinian structures. The cubic trend surfaces not only reflect the main properties of recent structures

but alsothe old structures in late Caledonian. The quadratic and cubic trend surfaces in south Suining areas show that the areas are located at the turning apex of a anticline.The residual trend axes are parallel to lineament of structural pattern (high residual axes parallel to anticline axes and lower ones to that of syncline)

and high residual axe are shifted slightly towards north due to regional tilting.Analysed the superficial structuer pattern in central Sichuan

the cubic trend residuals are selected for geological interpretation. The high residuals are normally the reflection of aeromagnetics

gravity anomalies or deep fractures. A Preliminary division is made on structural element of central Sichuan based upon the trend residuals.The fractures are well developed near the high residual axis lines. Distribution of commercial gas-sites within Xiangsi and Xianger gas pools in south Suining gas field coincide basically with the high residual axis lines on top of the Leikoupo Formation.