The aspect ratio of trenches is one of the key parameters in processing the HgCdTe infrared focal plane arrays (IRFPAS)．The divergence angle of the two-grid Kaufman ion-beam source that is widely used in China at present is typically large. Using such an ion beam source, the aspect ratio of HgCdTe isolation trenches is comparatively low. Several methods were employed in the etching process to increase the aspect ratio of trenches etched by Ar+ ion beam apparatus, such as with different types of photoresists, changing the incidence angle of ion beam, and utilizing three-grid Kaufman ion-beam source. The cross-section profile of the trenches on HgCdTe arrays was studied with scanning electron microscope (SEM ) and the aspect ratio was calculated. The influences of these methods on etching profiles were given and many results desirable for the design of high aspect ratio of ion beam etched trenches were achieved.