The invention discloses a method for determining a design coefficient of a reinforced thermoplastic pipe (RTP). The method comprises the following steps: analyzing an internal pressure load, bending load, external pressure load, axial tension load, temperature difference load and combined load of the RTP, and analyzing the load resistance of the RTP; establishing a limit state function, load probability model and resistance probability model under different load conditions; determining an average value, standard difference and variation coefficient of the loads and the resistance; giving a target reliability index, and determining a partial load coefficient and partial resistance coefficient by virtue of a FORM method; determining the design coefficient by virtue of an LRFD method. The method has the beneficial effects that the loads of the RTP are classified into the internal pressure load, the bending load, the external pressure load, the axial tension load, the temperature difference load and the combined load; the target reliability index is combined to form a calculation method for the design coefficient by establishing a limit state equation and establishing the probability models, so that a foundation is laid for the future engineering application of the RTP to an oil and gas transmission pipeline.