A Method for generation of Ncs set and a method for generation of random access preamble are disclosed. The method for generation of Ncs set comprises the following steps: determine an upper limit value Ncs_max of Ncs according to a maximum cell radius value which is required to be supported by a random access channel RACH, and select Ncs values which are less than or equal to the Ncs_max to be elements of an initial Ncs set; calculate a root sequence number Nr corresponding to each element in the initial Ncs set according to formula Nr=┌M/└Npre/Ncs┘┐; and delete elements in the initial Ncs set which have the same Nr value with other elements so as to generate a screening Ncs set in which each element has a different Nr value; if N, the number of the elements in the screening Ncs set, is greater than P, the number of maximum Ncs supported by the system, then delete N−P elements from the set so as to generate a final Ncs set; else regard the screening Ncs set as the final Ncs set; wherein, M is a preamble number required by each cell, and Npre is the length of preamble sequence.