Spread Spectrum TT&C system ranging accuracy is affected by pseudo code tracking performance of corresponding signals. Jamming maximum error (JME) expression of pseudo code tracking is derived to evaluate the impact of jamming on the pseudo code tracking at zero value point shift of the phase discriminator curves. Since JME requires the phase discriminator specific algorithm, second order central moment spread factor (SOCMSF) of the correlation curve mainlobe (CCM) for measuring the CCM distortion of the signal under jamming is proposed to assess the code tracking anti jamming performance. Simulation results show that theoretical analysis results are agreed with those from simulation and mainlobes SOCMSF, thus validating the JME expression and the proposed index could reasonably evaluate the impact of jamming on the pseudo code tracking.