It is a challenging work to develop lightweight humanoid robot arms, and the design process is usually slow due to the lack of specialized and systematic software. An IDE for the R&D of lightweight humanoid robot arm is proposed called ArmPlant which is ODE-based and mix-programed by using Visual C++ and Matlab. ArmPlant integrates such functions as shape and dimension design, mass distribution, joint torque evaluation, kinematics and inverse kinematics calculation, motion planning and simulation, human motion capture and reproduction, motion control, hardware driver, motion evaluation, etc. Thus it can be used for rapid development of humanoid robot arms. In practice, an 8-DoF humanoid robot arm is designed and implemented based on the platform. Two experiment scenarios, i.e., continuous grabbing and human motion tracking are selected to evaluate the overall function of ArmPlant and the motion characteristics of the robot arm. The experiment results in both simulation and prototype show that ArmPlant is fully-functional, accurate in computation and control, interactive, it supporting the whole development process of the lightweight humanoid robot arm and effectively improving the efficiency of the R&D process.