A novel random access (RA) preamble format is proposed in this paper to support fifth generation new ratio (5G NR) enabled satellite system, which is a low earth orbiting (LEO) based non-terrestrial network (NTN). Considering a fact that traditional design of RA preamble can not meet the link budget due to a long distance between the satellite and terminal on the earth, and also will cause a wrong or failure detection of PRACH, or wrong timing estimation for uplink synchronization. The frequency offset under the large relative moving speed between the satellite and the terminal will also increase the failure detection of PRACH (physical random access channel). Therefore, a novel RA preamble format, i.e., a Zadoff-Chu (ZC) sequence with multiple lengths, are designed. To reduce the ambiguous estimation of RA preamble, a symmetric transmission of the proposed preamble is analyzed. Further, two detection algorithms (Algorithm 1 and Algorithm 2) are proposed to detect PRACH. Simulation results validate that the proposed RA preamble can meet the LEO based NTN performance requirements. According to simulation results, it can be proved that Algorithm 2 is more robust, considering timing error and frequency offset.