If the e-juice is leaking from mouthpiece, firstly, please make sure the e-liquid was not filled into the air pipe. Secondly, please check if the sealing O-ringson the 
atomizer tube and atomizer head are both intact and in good condition.If the e-juice is leaking from the atomizer base, please check if the sealing o-ringson the atomizer
base is intact and in good condition and make sure the liquid level is between 10%-90%. Also you must make sure all parts of the atomizer are assembled tightly.