The basic mechanical properties and stress-strain constitutive relationship of polypropylene foam concrete (PPFC) were studied by orthogonal test. The results show that the cubic compressive strength, axial compressive strength and splitting tensile strength of PPFC specimens decrease with the increase of polypropylene fiber (PP) volume content (0.5%, 1.0% and 1.5%) in the range of test variables. With the increase of PP length (3, 6 and 9 mm), the cubic compressive strength, axial compressive strength and splitting tensile strength of PPFC specimens increase first and then decrease. The cubic compressive strength of PPFC specimens increases first and then decreases with the increase of fly ash (FA) mass content (40%, 45% and 50%), and the axial compressive strength and splitting tensile strength decrease with the increase of FA content. Based on intuitive analysis method, the optimal ratio combination of orthogonal test is A1B2C2, that is, the volume content of PP is 0.5%, the length of PP is 6 mm, and the mass content of FA is 45%. The failure mode of PPFC compression specimens is compression-shear failure. The failure cracks are mainly inclined cracks, accompanied by vertical cracks, and the failure surface is generally inclined failure. The failure modes of splitting tensile specimens are splitting failure, and the failure cracks are vertical cracks along the direction of load application. Based on the single factor variable method, it can be concluded that with the increase of PP volume content (0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% and 0.6%), the cubic compressive strength, axial compressive strength and splitting tensile strength of PPFC specimens increase first and then decrease. When the PP volume content is 0.2%, the cubic compressive strength, axial compressive strength and splitting tensile strength of PPFC specimens reach the maximum value of 16.00, 14.56 and 1.96 MPa, respectively. The apparent density has a linear relationship with the cubic compressive strength, axial compressive strength and splitting tensile strength of PPFC specimens. The stress-strain constitutive model of PPFC was established by piecewise expression.