A set of 4 in-vessel saddle coils are designed to generate a helical field onJ-TEXT tokamak to study the influences of external perturbation field to plasma.Thecoils will be fed with alternating currents up to 1 0 kA at frequencies up to 1 0 kHz.Dueto the special structure,thermal environment and limited space in the vacuum chamber,it is of great essential to make sure that the coils will not be damaged whenundertaking the huge electromagnetic forces in the strong toroidal field and theirtemperatures don’t rise too much to destroy the insulation.A 3D finite element modelis developed by the ANSYS code in this paper,stresses are analyzed in the worstcondition,then a mounting method is established.The results of the elastic and modalanalyses show that the mounting method meets the strength requirements.After that,athermal analysis is performed to study the cooling process and the temperaturedistribution of the coils.