The tunable source used in the synthetic aperture laser (SAL) radar is not s ufficiently stable while stable sources are not broadly tunable,leading to the fluctuations in the wavelength at the start of the scan,namely the starting wav elength error.In this paper,the effect of the starting wavelength error of the tunable source on the imaging of SAL is studied.An ima ging model of tunable laser output signal with starting wavelength errors is established.Th e simulation is carried out using MATLAB. The results show that the starting wavelength error deteriorates the azimuth ima ging but has no effect on the range resolution.The starting wavelength error has little e ffect on the main lobe amplitude of the azimuthal imaging.The main lobe is 2times and 1.5times of the ideal main lobe under uniform distributions of (0,2λ_c)and(0,λ_c) respectively.When less than (0,0,1λ_c),the effect of the main lobe wi dth can be negligible.There is still a significant effect on the side lobe.If less than (0,0．02λ c),the effect on the side lobe can be negligible.Furthermore,the nonlinearity of Doppler frequency caused by starting wavelength error is the reason that the azimuth imaging is de teriorated.