The effect of filtering on the suppression of time-delay signature in the output signal of the optical feedback chaotic semiconductor laser is studied experimentally. Under the condition of the chaotic signal 100 MHz and 500 MHz low pass filter, the peak values of the autocorrelation coefficient and the permutation entropy at the feedback round trip time are used to quantitative extract the time-delay signature. The time-delay signatures with various feedback strengths are measured at different bias currents. The results show that the filtering effect suppresses the time-delay signature of the chaotic signal effectively. Under the condition of 1.5Ith bias current and -7.5 dB feedback strength, the autocorrelation function near the external cavity delay decreases from 0.264 to 0.036, and the permutation entropy increases from 0.985 to 0.997. Meanwhile, the peak value of the autocorrelation coefficient at the feedback round trip time is inversely proportional to the permutation entropy with the feedback strength increasing. The results also show that the complexity and strength of chaotic laser first rise, and then fall with the increase of feedback strength. The filtering effect induces the complexity of chaos to approach the maximum under lower feedback strength, and the complexity remains unchanged with the feedback strength increasing. Moreover, the filtering can also improve the intensity distribution and enhance the symmetry of probability-density function, which leads to substantial increase in the rate of random number generators.