In this paper, we assume there exist no three-body forces in a baryon. So that the constraint equations for two particles Pi2+U(x2)+mi2=0 (i=1，2 )can be applied to the SU3 model of the baryon. Next, we take U(x2) as a+bx2. By use of a proper coordinate transformation, the internal motion of the baryon can be reduced to double covariant harmonic oscillators. From the Kustannheimo-Stiefel transformation, the problem of a covariant harmonic oscillator can be transformed to that of a threedimensional hydrogen atom with constranits. On that basis, the difficulty of the excitation of the time degree of freedom can be avoided naturally and the mass-squared formula for baryons can be obtained.