Abstract: The problem of approximate counting for large scale wireless sensor networks was studied. Two approximate counting algorithms, DBT-ACA and DBT-BACA, based on DBT (digital binary tree) protocol were also proposed. The algorithms presented could attain the counting result in time while meeting the accuracy requirement. DBT-BACA exploits binary search, level-by-level forwarding and delay response technique to effectively reduce the query delay and transmission cost. Theoretical analysis and experimental results show that the proposed algorithms outperform existing approaches in terms of estimation accuracy, time efficiency and energy cost.