Photonic nanojet (PNJ) is a tightly focused, non-resonant and spatially highly confined light beam that emerging on the shadow side surface of a light-illuminated lossless dielectric microparticle with a diameter comparable or slightly larger than the wavelength of the incident light. PNJ’s significant properties of subwavelength transverse beamwidth, high light intensity and propagation capability of extending evanescent field region make it get a lot of applications in a broad range of areas, such as optical signals enhancement, optical imaging, optical tweezers, optical data storage, optical waveguide, optical sensing, optical nanofabrication, optical switching, etc. The formation characteristics of the PNJ are depended on the geometrical morphologies and dielectric properties of the microparticles, the surrounding medium and the natures of illumination light. Over the past 15 years, PNJs generated from different structures (cylinder, sphere, ellipsoid, disk, cuboid, core-shell, multilayer, assembled nanofibles, etc.) were investigated. In this paper, a unique structure of D-shaped microfibers in terms of height (hD), width of D-sector (wD) and curvature radius (rD), which can be fabricated through optical fiber polishing and optical fiber tapering techniques, was presented and studied with a finite-element- based numerical method. Three different cases of hD < rD, hD = rD, and hD < rD were chosen as typical research models. The PNJ parameters of focal distance, full-width at half-maximum, decay length and maximum light intensity with respect to the variations of widths of D-sector and rotation angles were systematically analyzed. The research results provide a good insight to develop optical microprobes and optical microlenses with long working distance.