High accuracy surface modelling（HASM） constructed based on the fundamental theorem of surface is more accurate than the classical methods

but the computational speed of HASM is proportional to the third power of the total number of grid cells in the computational domain.In order to decrease the computational cost and improve the accuracy of HASM

this paper employed a modified Gauss-Seidel（MGS） to solve HASM.The fact that MGS is more accurate and faster than GS is proved in terms of theorem.Gauss synthetic surface was employed to comparatively analyze the simulation errors and the computing time of MGS and GS.The numerical tests showed that under the same simulation accuracy

MGS is faster than GS

and the time difference between MGS and GS is approximately proportional to the second power of the total number of grid cells.Under the same outer or inner iterative cycles

MGS is more accurate than GS.The computing time of MGS is proportional to the first power of the total number of grid cells.Compared with the direct methods for solving HASM

MGS greatly shortens the computing time of HASM.SRTM3（36°—37°N

107°—108°E） of Dongzhi tableland located in Gansu province was employed as a real word example to validate the accuracy of HASM based on MGS.In the example

about 50% of SRTM3 was used as validation points

the others for DEM simulation.The results indicated that RMSE of HASM based on MGS is about 2.4

1.8

1.3

2.7 times less than those of KRIGING

IDW

TIN and NEAREST.