In this paper, we propose a 36-quadrature amplitude modulation (QAM) superposition modulation technique that is featured with uneven symbol probability by nonlinear precoding, named nonlinear coded nonuniform superposition (NCNS) QAM. Its aim is to alleviate the nonlinearity effect caused by high instantaneous power in multi-input single-output (MISO) visible light communication (VLC) system, with an uneven probabilistic-shaped constellation. The transmitter includes two LEDs to send signals independently, and the receiver uses a photo detector to receive the superposed QAM signal. The experiment results show that NCNS has a better robustness against nonlinearity than pulse amplitude modulation 4, approximately gaining a 16% increase in maximum usable peak-to-peak voltage and a 33% enlargement in dynamic range area. It is a simple but effective approach to solve the bandwidth limits related to signal power and hopefully be applied in large power VLC systems such as underwater VLC, or to improve the robustness against power fluctuation.