In the field of optical engineering, microscopic imaging measurement is an important means of optical installation and adjustment. To realize correlated photon imaging measurement and auxiliary monitoring in the process of correlated photon radiation reference source optical path system installation and adjustment, it is necessary to establish a microscopic imaging system with a broad spectrum spanning of 360~1 000 nm. Some scholars at home and abroad have designed a series of finite conjugate or infinite corrected objective lenses with high numerical aperture, large field of view, broad spectrum coverage, high magnification, et al. There are also a variety of commercial microscopic objective lenses, but the correlated photons band to be measured is beyond the applicable band range of current commercial microscopic objective lenses. A broadband plan-apochromatic microscope objective was designed in this study. The design of broadband microscope objective needs to consider the problem of apochromatism firstly. The apochromatism of refractive microscope objective is mainly realized by the diffractive optical elements or the combination of different glass materials, the diffractive optical elements are not suitable for precision optical systems, so the glass combination method is used for the design of apochromatic microscope objective. Based on the basic apochromatic theory, the model of compact three-piece lenses was selected, then was realized through a program script with MATLAB? software. The glass material chooses domestic CDGM glass library. Firstly, according to the range of wavelength, glass production frequency, price, and other indicators of the glass library for initial screening, the original glass library has a total of 304 kinds of glass, the final remaining 25 kinds of glass after the initial screening. Then, the least square method is used to calculate the optimal focal power allocation of each glass combination, and the glass combination is selected by the sum of the absolute focal power and the corresponding minimum residual chromatic aberration. In the end, the glass combination with better secondary spectral correction effect is obtained. In addition, the influence of a commonly used special optical material, CaF₂, on secondary spectral correction was also studied. It is found that the introduction of CaF₂ will improve the total imaging quality. Although the color focal shift will be larger, the color focal shift can still meet the requirements. Finally, the combination of CaF₂, H-FK95N, H-LaF50B and H-LaF52 glasses was selected. By selecting an existing patent as the initial structure, an infinite-corrected and plan-apochromatic microscope objective and broad spectrum coverage with magnification of 20×, numerical aperture of 0.3, working distance of 10 mm, parfocal length of 60 mm, field of view of 0.66 mm and spectrum coverage of 360~1 000 nm was designed, without any aspheric sphere. The MTF curve, color focal shift, ray aberration, astigmatic field curves and distortion curves, longitudinal spherical aberration, RMS wavefront error and diffraction encircled energy distribution diagrams of the optical system were analyzed. The results showed that the MTF curve of the system was close to the diffraction limit at 80 lp/mm, the astigmatic field correction meet the international standard of flat field, and the other imaging indicators were also close to the diffraction limit. By sensitivity analysis in ZEMAX? software, the element tolerance, material tolerance and assembly tolerance of the microscope objective are reasonably allocated. The geometric MTF value at 80 lp/mm was selected as the evaluation indicator. After Monte Carlo analysis, the nominal MTF value of the microscope objective at 80 lp/mm was 0.887 9. In fact, there is an 80% probability that the MTF exceeds the value of 0.839 1, which means that the microscope objective can meet the requirements of image quality and manufacture. The design in this paper can provide technical reference for the design of the plan-apochromatic microscope objective, especially for the broadband apochromatic design.