This paper presents how to make use of the advantage of round-off error effect in some research areas. The float-point operation complies with the reproduce theorem without the external random perturbation. The computation uncertainty principle and the high nonlinear of chaotic system guarantee the numerical error is random and departure from the analytical result. Combining these two properties we can produce unilateral one-way function and provide a case of utilizing this function to construct encryption algorithm. The multiple-precision (MP) library is used to analyze nonlinear dynamics systems and achieve the code. As an example, we provide a scheme of encrypting a plaintext by employing the one-way function with Lorenz system. Since the numerical solution used in this scheme is beyond the maximum effective computation time (MECT) and it cannot satisfy the requirements of return-map analysis and phase space reconstruction, it can block some existing attacks.