Based on Galois theory of definite field, using the square prime sequence, the code function of basic prime code is modified and extended. The auto-correlation and crosscorelation of MSPC, which based on square prime sequence, are analyzed in detail. The maximum auto and cross correlation are 2 and 1 respectively. And then, going through reconstructing the prime sequence and code function, a novel signature code, ESPC has been acquired. Compared to basic OPCs derived from linear prime sequence, the maximum value of auto-correlation of ESPC is reduced from p - 1 to 1 and cross-correlation is reduced from 2 to 1. the ratio of auto-correlation peak to sideband has largely enhanced, which ensures a better system performance and is more advantageous in signal detection