RNGs(random number generators) are important building blocks for algorithms in security applications. They are paramount in construction of encryption keys. For security applications with key exchange in high frequency, the two RNGs provided by Linux kernel are not acceptable because of their low efficiency. An algorithms for fast pseudo random number generation as proposed is implemented in Linux user space. The source of random number is a high-frequency 64?bit counter. The lowest 4?bytes of the counter are added in a pool, then the pool is hashed with SHA(security hash algorithm). The first 16?bytes of the hash are output. This process is repeated until the requested number of random number is achieved. Several statistical tests are employed to investigate the randomness of RNGs. The results show that the quality of random number generated are guaranteed. Due to its running in Linux user space, this algorithm has much higher efficiency than Linux’s two RNGs.