In a double optical feedback semiconductor laser chaotic system, by fixing the feedback time and feedback strength of the one mirror (named as fixed cavity M1), the influences of the feedback time and feedback strength of the other mirror (named as tunable cavity M2) on the time delay feedback signatures of the chaotic system have been investigated experimentally. The results show that, for the case of the two cavities with identical feedback strengths, time delay feedback signatures of chaotic output can be suppressed efficiently when the cavity length of M2 is approximately equal (but can not exactly equal) to the cavity length of M1 (or half of the cavity length of M1). Fixing the length of M2 to approximately equal to the cavity length of M1 (or half of the cavity length of M1), the time delay feedback signature suppression can be further improved through adjusting the feedback strength of M2 carefully. Therefore, adopting a double optical feedback semiconductor laser chaotic system can make the system behave with higher security due to the efficient hiding of delay feedback parameter of the system.