A new type of optical element--combined axicon is proposed for generating non-diffracting Bessel beams.This element is designed with gluing positive and negative axicon.Its property is the same as single positive axicon for beam transformation,and equivalent conical angle is decided by the conical angle difference of positive and negative axicon.Therefore,we can get smaller conical angle by combining positive and negative axicon with comparatively large conical angle for each axicons,and also get non-diffracting beam with longer distance.The technical problem of the small conical angle which is hard to machining is solued.The ABCD matrix of the combined axicon is deduced.It shows that the combined axicon can transform plane wave to Bessel beam by numerical calculation.The optical field distribution behind combined axicon is also simulated by Zemax software,and compared with single positive axicon.Research results open a new way for generating non-diffracting Bessel beams.