Abstract: The effect of higher order multipole fields on the property of linear quadrupole mass filter were investigated with theoretical simulations. The decapole component A₅, or the mixture of decapole A₅, hexapole A₃ and octopole A₄ fields can be added to the linear quadrupole by using four special shape rods. The A₅ and some other higher order multipole fields can also be added to linear quadupole when four cylindrical rods with different diameters are used. The existence of some small amount of A₅ will change the shape of the first stability diagram, and distort the mass resolution of the linear quadrupole mass filter. When some hexapole A₃, and octopole A₄ field are added besides A₅, the mass resolution will be significantly improved.