In deep borehole parallel cut blasting,the length of the blast hole stemming is an important factor to determining the blasting effect.Too long or too short filling will weaken the cut blasting effect.In order to improve the blasting effect of deep borehole parallel cut blasting,based on the theory of rock fragmentation under the combined action of shock wave and explosion gas,by analyzing the relationship between the movement process of the stemming rushing out of the blast hole and the time required for rock fragmentation,the reasonable stemming in the cut is obtained.The calculation formula for the upper and lower limits of the length can determine the reasonable range of the stemming length.Three groups of model tests are carried out to analyze the blasting funnel,blasting pile quality and fragmentation produced by the test.The test shows that the stemming length of the experimental group with the best blasting effect in the model test is 20 mm,which is in the range of 19.86 mm to 22.07 mm of the reasonable stemming length calculated in theory.The reasonableness of the formula for calculating the reasonable stemming length range is verified.In view of the situation that the blasting gas passes through the empty hole due to the excessively long stemming,it is proposed to properly block the upper and lower ends of the empty hole in deep borehole parallel cut blasting to reduce this effect.