Abstract:According to the distribution feature of welding residual stress on plate with weldingseam along axis，a mathematical model of the welding residual stress is established. A fotmula of natu-de-- alltheral frequency of four boundary simply-supported quadrate thin plate with welding residual stress isveloped. Some conclusions have been obtained. 'THey are:(1)if there is welding residual stress  all natural frequencies of component are in increase，( 2 ) change of high ranknatural frequency under the influence ofresidual stress is larger ihaa that of low rank natural frequency. and the higher the rank number is，the larger the absolute amount of change of natural frequency is.

Key words: mathematical model  residual stress  natural frequency  welding  quadrate thin plate