A tightly focused laser beam can trap particles of size ranging from tens of nanometers to tens of micrometers.In the process,angular momentum is transfered from the traping beam to the traped particles and micro optical torque is generated.The calculation of the optical torqne is complicated.A method of using T-matrix to compute the optical torque is presented.Optical trap parameters affecting the torque is analyzed.Simulations prove the effiency of the T matrix and that offers a tool for the analysis of optical torque.