A positive lens, a negative lens and a diffractive optical element (DOE) can compose two kinds of hybrid diffractive-refractive telescope objectives when assembled differently. There is a different spherochromatism after the two systems correct secondary spectrum, spherical aberration and comatic aberration. Reasons of the different spherochromatism of the two configurations are researched by Seidel aberration analysis. And spherochromatism of the configuration with diffractive optical element placed on the negative lens is 7 times as much as that of the other. When the substrate of diffractive optical element is the negative lens, a solution is presented to decrease spherochromatism of the system, and the value of spherochromatism is decreased to 0.307 mm. A conventional apochromatic optical system is designed in addition, and compared with the hybrid diffractive-refractive apochromatic optical system. It shows DOE can substitute special optical material of conventional optical system and obtain the same imaging effect. The influence of diffraction efficiency on the imaging optical system by the polychromatic integrated efficiency of DOE is analyzed at last.