The electrical properties and characteristics of photoluminescence (PL) at 11K for InP implanted with Si+ at 200℃ have been studied. It has been found that the sheet electron concentration in Si+ simply implanted sample tends to a saturation level with increasing the Si+ dose, while that in Si++P+ dually implanted sample increases greatly. The 11K PL spectra reveals that there exists Sip-Vp complex in Si+ implanted InP, which can be inhibited by co-implanting P+. The mechanism of improved electrical properties by Si++P+ dual implants is, also discussed.