Abstract: The phenomena of unsmooth motion within a pneumatic cylinder at slow speeds is called the stick-slip.Stick-slip is observed in many applications causing troubles.The paper studies the stick-slip phenomena in an unsymmetrical cylinder driven by meter-out circuits,by using analytically dimensionless parameters according to the model of the system,and validating it with many experiments.The paper puts forward a simple criterion of stick-slip.In order to validate the validity and generality of the criterion,a series of experiments are made under different loads and velocities.The results showed that the criterion can correctly predict whether stick-slip will occur directly from working parameters.