An improvement for Quantum Random Numbers Generator (QRNG) scheme based on measuring laser phase noise is proposed, where several selectable branches is used instead of two fixed branches as in a traditional Mach-Zehnder Interferometer (MZI). The operation principle behind the improved scheme is discussed and the reason why the sampling rate of the improved scheme can break through that of the traditional MZI scheme without losing system entropy is analyzed. The operation time sequence of the optical switches and the system requirement of the improved scheme are also given. The results show that the limitation of laser coherence time is shifted to the requirement of the delay time in each branches and the sampling rate of the improved scheme can be multiple times of the traditional scheme.