In this research the Expressions that determine the eigenfunctions and modes eigenvalues in waveguides with a composite sectorial cross-section are obtained. The possibility of characteristics changing for eigenvalues by changing the parameters that characterizing the cross-sectional shape was studied. The field modes of waveguide based on Ritz method was analyzed.it was determined the characteristics of the quasi – H_mn modes in a cruciform sector waveguide, and quasi – H_mn modes in a composite sector waveguide with an arbitrary number of sectors.it was also shown the advantage of using the cross-section waveguide in single mode optical fiber wavelength range. The eigenvalues (χ) and the normalized coefficients (a )for quasi – H_mn modes in terms of Bessel functions (Q_m,P_m ) and their combinations was obtained.