This paper pointed out that we can determine the initialization x0 when the random sequence is generated by the piecewise linear chaotic map in finite precision, and aimed at solving this objection, an improved measure of perturbing the system variable timely is proposed, and an improved random number generator based on chaotic map is designed and realized. Meanwhile, their working process and theory are analyzed, and the simulation, validation and test of the whole system is finished, and the result indicated that the bit rates is up to 20 MHz and the random number could pass the FIPS140-2 randomness test.