Abstract: With the continuous increase of requirements in the reservoir production, it is difficult to effectively improve the producing degree of reservoirs and enhance the single well production only by increasing the length of horizontal well. The horizontal multilateral well which can increase the drainage area of reservoirs, improve the single well production, save drilling cost is considered to be the ideal well type for the efficient development of oil and gas reservoirs. However, there exists the possibility of sidetracking failure or overlong operation time spent even though the operation being successful, which is very contradictory to the high cost of offshore drilling operation. This paper summarizes the measures taken in the horizontal multilateral well by rotary steering tool in the East China Sea. Combined with the sidetracking practice, it is concluded that the key point for the successful operation of a horizontal multilateral well is that the operation should be conducted under the reasonable construction procedure, big dogleg slope be made ahead of the predetermined sidetracking point, which makes the new hole easier when sidetracking and improves the success rate of open-hole sidetracking.