Using two-step method InP epilayers were grown on GaAs(100) substrates by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). X-ray diffraction (XRD) and room-temperature (RT) photoluminescence (PL) were employed to characterize the quality of InP epilayer. The best scheme of growing InP/GaAs(100) heterostructures was obtained by optimizing the initial low-temperature (LT) InP growth conditions, investigating the effects of thermal cycle annealing (TCA) and strained layer superlattice (SLS) on InP epilayers. Compared with annealing, 10-period Ga0.1In0.9P/InP SLS inserted into InP epilayers can improve the quality of epilayers dramatically, by this means, for 2.6-micron-thick heteroepitaxial InP, the full-widths at half-maximum (FWHMs) of XRD 'omega' and 'omega'-2'theta' scans are 219 and 203 arcsec, respectively, the RT PL spectrum shows the band edge transition of InP, the FWHM is 42 meV. In addition, the successful growth of InP/In0.53Ga0.47As MQWs on GaAs(100) substrates indicates the quality of device demand of InP/GaAs heterostructures.