A technique for detecting Bragg wavelength shift using ordinary wavelength division coupler (WDC) as wavelength discriminator is presented. The WDC is used to transform the wavelength shifts to intensity changes. Double differential amplifiers are used to get rid of interference induced by light source and surroundings. LED is used as the source to reduce the system cost,so the demodulated source and AC amplifiers are available. The strain resolution of 10 με and temperature resolution of 0.2 ℃ are achieved in the experiment. This is one of the cheapest fiber Bragg grating sensors till now.