A switchable dual wavelength square noise like pulse is achieved from the linear cavity mode locked fiber laser based on nonlinear polarization rotation.By regulating the cavity parameters,square noise like mode locking at 1530 nm and 1563 nm are obtained from the fiber laser,achieving pulse durations of up to 12 ns and 26 ns,respectively.The corresponding maximum intracavity pulse energy can reach 14.7 nJ and 45.6 nJ,respectively.Additionally,the dual wavelength noise like mode locking can be also realized at the two wavelengths.The output pulse exhibits a step like shape with the pulse width of 5 ns,which could be attributed to the superposition of the square pulses at different wavelengths.The experimentaal results are helpful to further reveal the formation mechanism and characteristics of square noise like pulses in the linear cavity fiber laser,and provide a reference for the design of multi wavelength laser source with high energy.