One of the most important factors determines specifications of 4He optically pumped magnetometer is the quality of resonance signal given by sensor probe. This paper introduces a laser 4He optically pumped magnetometer using an ECDL laser. An external cavity length tuning system of ECDL laser based on the double light path atom saturated absorption spectrum method with a 4He cell is build up to ensure that an effective 1083.207 nm laser light source is provided for the magnetometer probe. It is designed a double path photoelectric detector to get the absorption peak signal by the difference technology. Because signal in accordance with Lorentz linear features, a detection method combined with first and second derivative of signal curve is proposed. Join a modulation signal whose form is dc component add sinusoidal component, the system make ECDL laser give a stable output wavelength around 1083.207 nm. With the laser light, a resonance signal with better quality than the 4He optically pumped magnetometer probe using the gas discharge lamp light source is given.