By a combination of the numerical iteration method and the intelligent optimization algorithm, the adaptive weight particle swam optimization with secant method (AWPSO—SM) was presented which was applied for solving the parallel mechanism forward kinematics problems. Then, the 3—UCU (U is universal pair, C is cylindrical pair) parallel mechanism was treated as the research object, and then the detailed solving process of AWPSO—SM was given, namely, the inverse kinematics model of 3—UCU parallel mechanism was established firstly;based on the model, the iterated function and fitness function was designed, and then the forward kinematics of the 3—UCU parallel mechanism was solved by AWPSO—SM.Finally, the effectiveness and accuracy of AWPSO—SM was verified via several numerical examples of 3—UCU parallel mechanism, 3—PPR (P is prismatic pair, R is revolute joint) parallel mechanism and 4—SPS (S is spherical joint) parallel mechanism which were the typical parallel mechanisms in Matlab environment. From simulation results, AWPSO—SM avoids the effects of the local convergence and the initial value on the calculation results, and could solve the forward kinematics of the 3—UCU parallel mechanism effectively. Moreover, AWPSO—SM avoids the complicated derivation process and has simple calculating process. AWPSO—SM has better accuracy with little iteration times and universality than AWPSO and secant method.