In this work, we present an nS _1/2→( n+ 1)S _1/2two-photon excitation EIT-AT spectrum of Rydberg atom in the vapor cell. A ground state (6S _1/2), a first excited state (6P _3/2) and Rydberg state (69S _1/2) of cesium atoms constitute a three-level system. A weak probe laser locking to the transition of 6S _1/2( F= 4)→6P _3/2( F′ = 5) couples the ground-state transition, and the strong coupling laser drives the Rydberg transition of 6P _3/2→69S _1/2to yield electromagnetically induced transparency (EIT) effect, which realizes the optical detection of Rydberg atoms. Two Rydberg 69S _1/2and 70S _1/2levels are coupled with the microwave field at a frequency of f _MW= 11.735 GHz, forming a microwave two-photon spectrum. To observe the influence of microwave electric field power on two-photon spectrum, we investigate the microwave coupled Rydberg EIT-AT spectra at different microwave fields. The measurements show that the EIT-AT splitting interval is proportional to the square of the microwave electric field at strong microwave field, and indicvates a nonlinear dependence at weak microwave electric field. The theoretical calculation accords with the experimental measurement. The work here is of significance in precisely measuring the microwave electric field.