Study of ion guiding effect of capillaries in insulator is of significance for developing passive-type ionic optics. Interactions between ions with different values of Ep/q, such as 150 keV O3+, 0.32 MeV O+ and 2 MeV O2+, and alumina capillaries are investigated. For projectile ions of 150 keV O3+, a guiding effect exists during the passage of the projectile ions through the capillaries. As the capillaries are tilted with respect to the projectile ion beam, the projectile ions can still pass through the capillaries considerably and the charge state remains unchanged; the spectrum of angular distribution of the ions out of the capillaries shifts by an angle the same as the tilt angle of the capillaries; the penetrating rates of the projectile ions for different tilt angles of the capillaries can be fitted to Gaussion function. For 0.32 MeV O+ and 2 MeV O2+ ions impinging on alumina capillaries, no guiding effect occurs in the interaction process. The maximum value of Ep/q of the projectile ions for guiding effect to occur is less than 320 kV.