A denoised and wide swath thermal imaging technology based on low rank matrix approximation (LRMA) was proposed to solve the problem of low signal-to-noise ratio (SNR) of thermal imaging system noise in strong background and weak signal scene. This technology utilized array whisk broom mode to realize wide swath imaging and construct strict observations. The denoising low-rank matrix of observations was solved via weighted nuclear norm minimization (WNNM). Experiments showed that the technology had high peak signal to noise ratio (PSNR) and denoising robustness. Both of imaging width and detection sensitivity were improved. The technology has certain application value in the field of weak target recognition and large area investigation.