There are some questions and present condition existing in the cost of construction at present Such as: the budgetary estimate beyond the estimate, the budget beyond the budgetary estimate, the fimal accounts beyond the budget. We find out the jnfluence which has different cost of construction in different stage of engineering development under the construction. We also find out the problems existing in the reality of construction at present. We mainly probe into all those influences and problems from the period of decision, the period of designing.