We experimentally demonstrated a frequency locking method for Rydberg transition laser without modulation by using electromagnetically induced transparency (EIT) spectroscopy in room temperature Rb vapor cell. The cascade three-level system of Rb atom consisted of ［EQUATION］, ［EQUATION］, and ［EQUATION］, where the probe laser excited the atoms in ground state ［EQUATION］to intermediate state ［EQUATION］and the coupling laser was usedto drive the atoms transition from intermediate state ［EQUATION］to Rydberg state ［EQUATION］. In the experiment, the probe laser was locked by saturated absorption spectroscopy (SAS). The EIT signal was monitored by scanning the frequency ofthe coupling laser and measuring the intensity of the probe laser. The probe laser frequency was modulated and the error signal was obtained by demodulating the EIT spectrum. In order to achieve the frequency locking of coupling laser, we feedbacked the error signal to the laser via the PID control circuit. Finally, a modulation-free frequency locking of the coupling laser is realized. Comparing with the traditional method where both two lasers need modulating, here only one laser need modulating. In this case, the frequency perturbation caused by modulation signal is suppressed and the long-term stability of frequency locking system can be improved. Thus, we realized the laser frequency locking without modulation and measured the frequency jitter after locking with the result about 1 MHz. The Allan variance was used to analyze the error signal. The Allan variance reached the minimum value in about 1 minute with the value of about ［EQUATION］when coupling laser was locked.