Random access algorithm is critical for the performance of interactive broadcasting system. Random access with Dynamic Window Size and Random Access Slots(D-WS-RAS) is proposed as an efficient way to tackle this problem in the interactive broadcasting system. This algorithm is composed of three parts: utilize Bayes' rule to estimate the number of access, dynamically set backoff window size and dynamically adjust the number of random access slots within a frame. And we examine the performance compared with traditional Uniform Backoff (UB) algorithm in terms of retransmission delay, packet-dropping delay and system throughput Results show that D-WS-RAS outperforms UB algorithm and simple algorithm with dynamic window size.