An Euler wavelets method is proposed to solve a class of nonlinear variable order fractional differential equations in this paper. The properties of Euler wavelets and their operational matrix together with a family of piecewise functions are first presented. Then they are utilized to reduce the problem to the solution of a nonlinear system of algebraic equations. And the convergence of the Euler wavelets basis is given. The method is computationally attractive and some numerical examples are provided to illustrate its high accuracy.Many phenomena in fluid mechanics, chemistry, physics, finance and other sciences can be described successfully by models using mathematical tools from fractional calculus, i.e. the theory of derivatives and integrals of fractional order [Miller and Ross (1993)]. Due to the fractional order exponents in differential operators, analytical solutions of fractional equations are usually difficult to obtain. Consequently, different methods have been developed to give numerical solutions for fractional equations, including fractional differential transform method [Wei and Chen (2014)], Adomian decomposition method [Song and Wang (2013)], Chebyshev pseudo-spectral method [Khader and Sweilam (2013)], Homotopy perturbation method [Abdulaziz, Hashim and Momani (2008)], Homotopy analysis method [Dehghan, Manafian and Saadatmandi (2010)], and wavelet method [Li and Zhao (2010); Wang and Fan (2012); Wang and Zhu (2016)]. Recently, the concepts of fractional derivatives of variable order have been introduced and some research works of the relative practical applications have arisen [Sun, Chen and Chen (2009); Samko (2013)]. Several numerical approximation methods are proposed to solve the variable order fractional differential equation [Chen, Liu, Li et al.