An equation of the Bethe-Salpeter type is used to obtain the internal wave function of mesons. It is found that if the potential well between the straton and anti-straton is of the pseudo-scalar type, then the 0- and 1- mesons will satisfy the same approximate radial wave function, and thus lead to SU6 symmetry. We have shown previously that pseudo-scalar potential is the only single type of potential which leads to this symmetry. The potential is V = V0+ V1, where V0 represents a super-strong deep well, the effect of which is to reduce the very large mass M of the free straton to a small effective value. The motion of the straton inside the meson is therefore relativistic. V1 represents a small potential of the order of 1/M of a simple harmonic oscillator. A tensor force is also introduced to account for the splitting of energy levels of the states with the same spin and orbital angular momentum. Our solutions for the ground and angular excited states of 0- and 1- mesons practically explain all the observed meson states. Our theory can apply equally to the baryon states if the phenomenological potential V0 is reduced by a factor of 2.