The work aims to lay a foundation for predicting corrosion rate of steel for 42CrMo drilling tool use by studying its corrosion behavior provided with different Cl? concentration at normal temperature. Average corrosion rate and electrochemical characteristics of 42CrMo in NaCl solution of different concentrations (mass concentration, applicable to the full text) were studied by immersion experiment and electrochemical testing technology, and lacing film specimen was analyzed with scanning electron microscope after 58 h immersion. Immersion experiment analysis showed that corrosion rate of 42CrMosteel reached a maximum of 0.124 g/(m2?h)when the Cl? concentration reached 60 g/L, the corrosion rate decreased gradually as the Cl? concentration increased when the Cl? concentration increased gradually (more than 60 g/L). Open circuit potential Eocp analysis showed that Eocp tended to decline as a whole with the increase of Cl? concentration, and showed clear tendency toward corrosion. Polarization curve analysis showed that slope of cathodic polarization curve was significantly higher than that of anode, and the corrosion current density reached the maximum 5.952 35 μA/cm2, in 60 g/L NaCl solution. Corrosion morphology study of 42CrMo showed that the surface corrosion products were unevenly distributed and subject to local pitting after 58 h immersion. Average corrosion rate of 42CrMo steel first increases and then decreases as Cl? concentration increases continuously, and it reaches the maximum when the Cl? concentration is 60 g/L. 42CrMo steel in static state at room temperature is mainly subject to local pitting in high content of Cl? solution, and the electrochemical corrosion process is mainly controlled by cathodic oxygen depolarization.