The typical interior alpine catchments in the Qilian Mountains in the northwestern China are selected for this study. Linear multi regression of monthly streamflow model is used for analysis. Five parameters: monthly streamflow, precipitation and air temperature of the former month and monthly precipitation and air temperature are chosen as the effective factors. Regressive coefficients are treated by standardized methods. Then standard coefficient matrix and effective factor matrix have obtained. Size and symbol of the elements in matrix may determine the extent of various ingredients affecting the streamflow. The methods of standard coefficient and effective factor are used to analyze the main ingredient affecting streamflow. The standard coefficient method is more intuitional than normal method. The streamflow factor method can eliminate false, which gives quantitatively the size of the effect factors. By the above analyses, the following results in the selected catchments in the Qilian Mountains may be found: (1) The baseflow may be effective on the alpine streamflow through November to April or May of the next year. (2) Effect of precipitation on the alpine streamflow is obviously strengthened with increase of precipitation from June to September. Meanwhile, precipitation becomes the most effective factor on the streamflow instead of subsurface water. (3) In comparison with the records of the stations in proluvial fan, the effective factor in the inner mountain has its special features. Firstly, effect of precipitation on the streamflow appears much more earlier in the inner mountain and it is dominant in May. Secondly, effect of air temperature is apparent in April and it is more important than the baseflow. (4) Effect of air temperature can not be neglected, especially from February to April, the melting season of snow cover. (5) In September, the streamflow is only related to precipitation, probably caused by change of contribution of underlying surface. Saturated soil, after rainy season (June to August), makes the increases of runoff, and effect of precipitation on the streamflow in September reaches its maximum.