The problem of low optical power level in PON network is becoming more and more serious with the development of FTTX service（long distance and large optical splitting ratio）. Through the analysis of the causes of the low optical power level

we analyse the main factors which affect the optical power budget. By comparing the standard defi nition and the practical application which based on the extended oam of EPON protocal /OMCI of GPON protocol

we also report the detection method of ONU transmit/ receive optical power and the corresponding weak optical fault location strategy. Finally some protection methods and solutions of low optical power level are summarized by engineering application.