|| It is a matter of burning question to foster pupils' thinking faculty of which is enable to give them a motive power for creations. In mathematics Course of study, fostering the thinking faculty is equal to fostering the "mathematical way of thinking". The "mathematical way of thinking" for pupils could be brought up by the way of learning through the mathematic actions dealing activities such as quantities and figures through or matters with tries and errors. In this research, for the pupils of the 4th grade mathematics unit "Decimal", We are to investigate to find the fittest practical teaching method through the effective teaching procedures of self-thinking faculty is, as the "mathematical way of thinking" by analyzing the main teaching purposes of "Decimal" unit. Secondly, We are to try to find the best way of "mathematical activities" as to develop the "mathematical way of thinking". Finally, through the comparing the results on each of the phases so called "self-thinking" and "self-actuating" place from the view of the "mathematical way of thinking", and at the same time, We are to check the effect of this teaching stratages we have done so far.