The future elastic optical network requires that the transmitter of the source node can dynamically change the modulation format and symbol rate of the transmission signal according to the transmission performance of the link and the diversified needs of users. A simplified two-stage intensity characteristic modulation scheme recognition algorithm is proposed. In this algorithm, quadrature phase shift keying(QPSK) signals are distinguished by Godard's error, and then 16 order quadrature amplitude modulation(16QAM) and 64QAM are further distinguished by intensity noise variance. The results show that when the minimum optical signal to noise ratio(OSNR) value of high-order modulation format signals such as physical data model-quadrature phase shift keying(PDM-QPSK), PDM-16QAM and PDM-64QAM is lower than 7% forward error correction(FEC) theoretical threshold(error rate is 3.8×10-3), 100% correct recognition rate can be achieved, and the number of symbols required by the proposed scheme is relatively small.