The common techniques used for sensing microwave power are based on diode detectors. The diodes used for detecting microwave power feature the advantages of wide dynamic range and high sensitivity. But when a low power level microwave signal is applied to a diode detector, the output is a DC or lowfrequency voltage with very low amplitude, which is effected greatly by all kinds of noise. This paper firstly discussed the diversity of noise resources. And then according to these causes, several weak signal detecting techniques are integrated to sensor the low power level in a creative way. The innovative methods involve the detecting circuits, chopping amplifier and data acquisition and so on. The results show these methods can dramatically improve the microwave power measurement sensitivity and accuracy. These methods have been deployed into a new model power measurement instrument and the effects are obviously great.