  A two dimensional system with extra degrees of freedom, such as spin and
valley, is of great interest in the study of quantum phase transitions. The
critical condition when a transition between different multicomponent
fractional quantum Hall states appears is one of the very few junctions for
many body problems between theoretical calculations and experiments. In this
work, we present that uniaxial strain induces pseudospin transitions of
composite fermions in a two-dimensional hole gas. Determined from transport
behavior, strain along <111> effectively changes pseudospin energy levels. We
deduce that diagonal strain dominates these variations. Our experiment provides
a wedge for manipulating two dimensional interacting systems mechanically.
