To investigate the uniaxial tensile mechanical properties of high-early-strength high ductility concrete （HES-HDC） at different PE fiber diameters and volume fractions， 17 groups of thin-plate specimens were designed and loaded under uniaxial tensile tests. The effects of PE fiber diameters （22 μm and 25 μm） and fiber volume fractions （1.00%， 1.25%， and 1.50%） on stress-strain curve， tensile strength， and strain of HES-HDC specimens at different curing ages （2 h， 24 h， 7 d， 28 d and 56 d） were investigated. A tensile toughness evaluation method suitable for the characteristics of HDC was proposed based on the test results. The results show that the HES-HDC stress-strain curve exhibits strain-hardening characteristics under uniaxial tensile loading， and the failure process is carried out with multiple cracks. The tensile strength and strain of HES-HDC at 2 h reach over 3.29 MPa and 0.88%， respectively， and the tensile strain at 28 d could remain more than 1.28%. When the fiber volume fraction is 1.00%， small-diameter fiber is beneficial to the tensile strain of specimens， while large-diameter fiber is beneficial to the tensile strength of specimens. Considering the tensile strength and strain of specimens with large-diameter fiber， the optimal fiber volume fraction is 1.25%. The proposed tensile toughness evaluation method can evaluate the tensile toughness of HDC during its whole loading process. In addition， the tensile toughness index of HES-HDC decreased with the increase of curing age， while the tensile strength coefficient increased. The tensile toughness of specimens with small-diameter fiber is higher than that of specimens with large-diameter fiber. The tensile toughness of specimens is the highest when the fiber volume fraction is 1.25%.