This paper presents a low insertion loss low-pass filter based on the spoof surface plasmon polariton (SSPP) with single comb-shape. Compared with traditional ones, the proposed filter provides lower insertion loss and return loss by optimizing the structural parameters of the mode conversion and SSPP parts. According to the measurement results, the average insertion loss of the fabricated filter is 0.41 dB and the return loss of which at the near-zero-hertz band is <−25.9 dB. The S parameter comparison result between the unoptimized and optimized filters demonstrates that the optimized filter provides lower insertion loss and return loss, smaller size, and better out-of-band rejection. The dispersion comparison result reveals the reasons behind the improved performances. The better performances of the optimized filter proves that breaking the regularity of traditional SSPP filters is beneficial to the filter's performances.